gralloc: stub out IMapper@4.0::lockYCbCr in C2Allocator

IMapper 4.0 does support lockYCbCr functionality through lock and
BufferMetadata getters. However, we will wait to add the support in
one central gralloc library. For now just stub out the call so
there aren't any compiler errors. Also, bytesPerPixel/bytesPerStride
can be gotten through BufferMetadata getters so they are no longer
supported in lock.

Bug: 141631415
Test: Compiles
Change-Id: I8b8adea765c42d7adac7ba86a3ce7ddd2751e8a0