Rename Gralloc0Allocator to Gralloc0Hal and make it inherit from
AllocatorHal. Do the same to Gralloc1Allocator. Add GrallocLoader
to load either of Gralloc[01]Hal and create a IAllocator instance.
Test: boots and VTS
Change-Id: I09ae680c0086ca9e73e412a34d7cd2f3665d3bc2