android-emugl: Move m_rcDec from RenderThread to RenderThreadInfo.

For some possibly historical reason, the renderControl decoder state
named |m_rcDec| was located into the RenderThread class, instead of
the RenderThreadInfo one, like the GLESv1 and GLESv2 ones.

This patch fixes the glitch by moving its declaration to
RenderThreadInfo and adjusting use sites.

+ Update documentation

Change-Id: I1c84e2bf05b93c46680c7fe33d804ccb1c041348
android-emugl: Rename ThreadInfo.h to RenderThreadInfo.h

Rename the header to match the class declaration it contains.

Change-Id: I1af5dd3cf4a1de0c32a136929966333822958d00
Merge changes I1af5dd3c,I1c84e2bf

* changes:
  android-emugl: Rename ThreadInfo.h to RenderThreadInfo.h
  android-emugl: Move m_rcDec from RenderThread to RenderThreadInfo.