[mlir][spirv] Allow controlling subgroup size

This commit extends the `ResourceLimitsAttr` to support specifying
a minimal and maximal subgroup size, and extends `EntryPointABIAttr`
to support specifying the requested subgroup size. This is possible
now in Vulkan with the VK_EXT_subgroup_size_control extension.
For OpenCL it's possible to use the `SubgroupSize` execution mode
directly.

Reviewed By: ThomasRaoux

Differential Revision: https://reviews.llvm.org/D138962