make sure to reject incompatible buffers in special function
GRALLOC_MODULE_PERFORM_CREATE_HANDLE_FROM_BUFFER
we use ioctl(PMEM_GET_SIZE) to validate that the given buffer is indeed
a pmem buffer.
add a way to convert a mapped "pushbuffer" buffer to a gralloc handle
which then can be safely used by surfaceflinger
also make sure to not send empty rectangles to the MDP.