Unable to use cloudfront origin-response eventType if memorySize or timeout exceeds 128 and 5
# Bug Report

## Description
### What did you do?
In setting up an image resize lambda function in the origin-request of a cloudformation distribution with AWS.Rekognition and sharp. This function consumes more than 128Mb and takes more than 5 seconds on every case. 
My `serverless.yml` file looks something like this:
```yml
...
functions:
  originResponseFunction:
    handler: originResponseFunction/index.handler
    timeout: 30
    memorySize: 896
    events:
      - cloudFront:
          eventType: origin-response
          origin: ${self:custom.origins.${self:provider.stage}}
...
```

### What happened?
When I run the command `sls deploy` I get the follwing error message:
```
  Error --------------------------------------------------
 
  Error: "originResponseFunction" memorySize is greater than 128 which is not supported by Lambda@Edge functions
      at serverless.service.getAllFunctions.forEach.functionName (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/lib/plugins/aws/package/compile/events/cloudFront/index.js:46:17)
      at Array.forEach (<anonymous>)
      at AwsCompileCloudFrontEvents.validate (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/lib/plugins/aws/package/compile/events/cloudFront/index.js:42:47)
      at BbPromise.reduce (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/lib/classes/PluginManager.js:505:55)
      at tryCatcher (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/node_modules/bluebird/js/release/util.js:16:23)
      at Object.gotValue (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/node_modules/bluebird/js/release/reduce.js:168:18)
      at Object.gotAccum (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/node_modules/bluebird/js/release/reduce.js:155:25)
      at Object.tryCatcher (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/node_modules/bluebird/js/release/util.js:16:23)
      at Promise._settlePromiseFromHandler (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/node_modules/bluebird/js/release/promise.js:547:31)
      at Promise._settlePromise (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/node_modules/bluebird/js/release/promise.js:604:18)
      at Promise._settlePromise0 (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/node_modules/bluebird/js/release/promise.js:649:10)
      at Promise._settlePromises (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/node_modules/bluebird/js/release/promise.js:729:18)
      at _drainQueueStep (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/node_modules/bluebird/js/release/async.js:93:12)
      at _drainQueue (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/node_modules/bluebird/js/release/async.js:86:9)
      at Async._drainQueues (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/node_modules/bluebird/js/release/async.js:102:5)
      at Immediate.Async.drainQueues [as _onImmediate] (/home/winstonwp/.nvm/versions/node/v10.16.0/lib/node_modules/serverless/node_modules/bluebird/js/release/async.js:15:14)
      at runCallback (timers.js:705:18)
      at tryOnImmediate (timers.js:676:5)
      at processImmediate (timers.js:658:5)
      at process.topLevelDomainCallback (domain.js:126:23)
```

### What should've happened?
For the time being I'm setting the lambda function manually in my AWS CloudFront Distribution, and I'm able to configure the `originResponseFunction` with a memorySize of `896Mb` and `30s` timeout.
Running `sls deploy` should allow me to deploy an `eventType: origin-response` lambda function with greater `memorySize` and `timeout` values.

I've identified a possible solution for this issue and will be happy to submit a Pull Request, but I'm not certain of what approach should I use, a `disableValidation` flag or an exception for `eventType: origin-response` when running the  [validate](https://github.com/serverless/serverless/blob/dc7413cee4392946253b153e6bf4d32d074bd8b5/lib/plugins/aws/package/compile/events/cloudFront/index.js#L41) function.