this gralloc module is only used on the emulator or without a h/w
renderer. therefore there is no synchronization to do in lock/unlock
and pmem buffers are not relevant.
hopefully this will remove some of the confusion about how gralloc
should be implemented and make it more obvious that this implementation
is not intended to be used by h/w renderers.
- make sure to return an error if a buffer is locked twice or unlocked while not locked.
- added registerBuffer() and unregisterBuffer() to the gralloc module so that we can do some cleanup when a buffer is no longer needed. this became necessary after we removed map/unmap so we have a place to unmap buffers without the need of a kernel module.
- change the constants for GRALLOC_USAGE_SW_{READ|WRITE}_NEVER to 0, so that NOT specifying them means "NEVER".
