[mlir][spirv] Relax restriction on pointer type for CooperativeMatrix load/store

This change allow CooperativeMatrix Load/Store operations to use pointer type
that may not match the matrix element type. This allow us to declare buffer
with a larger type size than the matrix element type. This follows SPIR-V spec
and this is needed to be able to use cooperative matrix in combination with
shared local memory efficiently.

Differential Revision: https://reviews.llvm.org/D84993