configure: add option --enable-vp8-role-name, default off (chromium)

1. when --enable-vp8-role-name is not set (default)
   vp8 decoder uses "video_decoder.vpx" as role name, it matches chromium
2. when --enable-vp8-role-name is set,
   vp8 decoder uses "video_decoder.vp8" as role name, it matches gst-omx

Change-Id: I7beab20397c9fa39255f1ab1c495b398b58a6f96
update output port param for resolution change

paramPortDefinitionOutput.nBufferSize is used by client
to alloc output buffer (gst-omx for example).
chromium doesn't care of it, getDecodedBuffer uses
sizeof(VideoRenderBuffer) when bNativeBufferEnable is true.
even sizeof(VideoRenderBuffer) seems too big,
since only one pointer is set to pBuffer->pPlatformPrivate.

1. Output.nBufferSize inits to OUTPORT_BUFFER_SIZE
2. calculate Output.nBufferSize in HandleFormatChange
3. if decoder gets frame size during start,
   does HandleFormatChange in ProcessorInit

Change-Id: Ieb1c14be1a36fc853db4ae1ed360a7d65ce7cdc6