[AMDGPU] Move dynamic VGPR allocation granules to TargetParser
Extend getVGPRAllocGranule with a dynamic block size and preserve the
fixed gfx90a-family granule. Remove the BaseInfo counterpart and migrate
its occupancy, scheduler, frame lowering, and register-block callers.
Cover dynamic allocation, static mode, and gfx90a-family exceptions.
Change-Id: Id441ddcea2d7a33121ddb4139af4c5f52f273ff3