Add gralloc usage conversion functions

Converting gralloc1 / ..graphics.allocator@2.0 usage to gralloc0 usage
requires more than just ORing bits and truncating: the CPU_READ_OFTEN
bits don't match up correctly. Add utility functions for converting
back and forth which handle this properly.

Test: boot bullhead-eng
Change-Id: I1cee972feaea486d5607c60acead2e870c2c9549