gralloc: require locked buffers follow format

Clarify that buffers that are locked (mapped) to the CPU must
be in the format requested in their BufferDescriptorInfo.
The buffers should not be compressed/swizzled/tiled/etc.

Bug: 141631415
Test: This is already assumed by the tests.

Change-Id: Ie674117418aaefc3f99ac2bc89c3da4072e236ec