[mlir][spirv] Remove layout decoration on unneeded storage classes

Per SPIR-V validation rules, explict layout decorations are only
needed for StorageBuffer, PhysicalStorageBuffer, Uniform, and
PushConstant storage classes. (And even that is for Shader
capabilities). So we don't need such decorations on the rest.

Reviewed By: hanchung

Differential Revision: https://reviews.llvm.org/D124543