Changes

** If the new write lock attempt is using the same handle to the gralloc buffer that is already locked, this will fail. This typically gives a message like "trying to upgrade a read lock to a write lock".

** If the new write lock attempt is using a different handle than the one already locked, then this locking operation will wait until the existing lock is released.

Genlock is implemented in the kernel. The kernel GL driver is able to lock and unlock directly. Typically, it will place a read lock on any gralloc buffer that's bound to a texture it's sampling from, and unlock when it's done with that texture.