[cooja-platform] Include eeprom.h to avoid implicit declaration warning
[cooja-platform] Remove unused variable 'shortaddr'

This variable was set but never used in the code
[cooja-platform] Add cast to linkaddr_t to avoid warning
[cooja-platform] Fixes for slip-bridge compatibility

* Added dev/uart1.h header file to cooja platform
* Added slip arch stub
* Suppress examples putchar definition as cooja platform provides its own

Note that the uart1.h file should only be an intermediate solution.
A generic contiki-wide definition for uart handling is required as each
platform defines its own varying set of uart functions.
Merge pull request #846 from ejoerns/pull-req/cooja-platform

Cooja platform fixes