Provide a mechanism for adjusting RSCompilerDriver after construction.

We add a simple callback to the reference implementation of libRSDriver.so,
such that additional BCC flags can be toggled/adjusted before doing any
actual CPU compilation.

(Cherry-picked from commit b1e577be646159113e1302d6d37a13751f78d2c5.)

Change-Id: If8e7e6cfc4ad4810890ca9e82969c695f39ca60b
Implement MemChunk::registerAllocFreeCallbacks().

This function allows a driver implementation to register its own handler
for allocating/freeing MemChunk objects. MemChunk is primarily used by
the ELF loader for various code/data segments.

(Cherry-picked from commit 37c0c8c44c1cc0ca9e79f28563fb062598faafe5.)

Change-Id: I94fedfb9fde0c2e686b9ddae31eb45a1fea37801
Add Sampler custom alloc/delete

(Cherry-picked from commit 8725468a009ca71e65d518cfa948ea75437db0de.)

Change-Id: I9085ee083a3ab0045b9aeb49ed525da4b8532b86