spirv/nir: Add support for OpAtomicLoad/Store
spirv/nir: Add support for OpAtomicLoad/Store

Fixes new CTS tests :

dEQP-VK.spirv_assembly.instruction.compute.opatomic.load
dEQP-VK.spirv_assembly.instruction.compute.opatomic.store

v2: don't handle images like ssbo/ubo (Jason)

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

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler