spirv/nir: Implement OpAtomicLoad/Store for shared variables
spirv/nir: Implement OpAtomicLoad/Store for shared variables

Missing bits from 2afb950161f847d9b0a7be03dfb62cacc5ea51ba.

Signed-off-by: Lionel Landwerlin <9463032a5b99ffad10f36631678a833369a311b5@intel.com>
Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler