[MLIR][GPUToLLVMSPV] Use `llvm.func` attributes to convert `gpu.shuffle` (#116967)

Use `llvm.func`'s `intel_reqd_sub_group_size` attribute instead of
SPIR-V environment attributes in the `gpu.shuffle` conversion pattern.
This metadata is needed to check the semantics of the operation are
supported, i.e., it has a constant width and its value is equal to the
sub-group size.

As the pass also converts `gpu.func` to `llvm.func`, adding a
discardable attribute of name `intel_reqd_sub_group_size` attribute to
the latter is enough for this pattern to work.

We no longer have a notion of "default" sub-group size, so this
attribute needs to be set in the parent function for `gpu.shuffle`
operations to be converted.

Drop dependency on the SPIR-V dialect as we no longer require creating
attributes from this dialect to lower `gpu.shuffle` instances.

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Signed-off-by: Victor Perez <victor.perez@codeplay.com>