spirv/nir: Implement OpAtomicLoad/Store for shared variables

Missing bits from 2afb950161f847d9b0a7be03dfb62cacc5ea51ba.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
1 file changed