[mlir][NFC] Rename MemRefType::getMemorySpace to getMemorySpaceAsInt
Just a pure method renaming.
It is a preparation step for replacing "memory space as raw integer"
with more generic "memory space as attribute", which will be done in
The MemRefType::getMemorySpace method will return Attribute and
become the main API, while getMemorySpaceAsInt will be declared as
deprecated and will be replaced in all in-tree dialects (also in separate
Reviewed By: mehdi_amini, rriddle
Differential Revision: https://reviews.llvm.org/D97476