[AMDGPU][SIMemoryLegalizer] Combine GFX10-11 CacheControl Classes (#168058)
Also breaks the long inheritance chains by making both
`SIGfx10CacheControl` and
`SIGfx12CacheControl` inherit from `SICacheControl` directly.
With this patch, we now just have 3 `SICacheControl` implementations
that each
do their own thing, and there is no more code hidden 3 superclasses
above (which made this code harder to read and maintain than it needed
to be).