hwc: Fix the copybit threshold comparison

Change-Id: Ife9d54d4592e2427e8de6e67b4c8f62b676b2679
libcopybit: protect all c2d copybit API's

- Each client API exposed by the copybit C2D needs
  to be protected.
- Add protection for clear_copybit and blit_copybit
- This is needed as clear_copybit was overriding the
  mapped gpuaddr while copybitwaitthread was waiting
  for transaction to finish and unmap
- After waitforTimestamp, the new addresses were
  unmapped leading to GPU Page fault

Change-Id: Ieeac10e73b05d3b47e602b2de4b4e64892737c9c
CRs-fixed: 470430

Conflicts:
	libcopybit/copybit_c2d.cpp
copybit: Fix type conversion error for GCC 4.7

GCC 4.7 has stricter type conversion rules

Change-Id: I699cfe1ceafb5728fb8e6f34f7b1996d3c812e7e
libcopybit: Fix potential memory and surface leaks in c2d

- Check MAX_SURFACES while mapping GPU addr
 --- While mapping gpu address, first check if the request
     is less than the MAX_SURFACES allowed.
 --- Without this check, when the request exceeded MAX_SURFACES,
     there was memory leak as that gpu addr was not unmapped
- Map the destination surface only once
 --- The destination surface for the c2d blit will be the
     FRAME_BUFFER_TARGET per transaction
 --- Map this only once from the copybit_clear which is the first
     call by hwc for a transaction
- Increase MAX_RGB_SURFACES to 12
 --- To handle use cases where there are more than 8 RGB layers

Change-Id: Iffacde30ee88b9c21d0895cb1922aa981bb079e9
CRs-fixed: 475327