nir: handle some 64-bit integer conversions
nir: handle some 64-bit integer conversions

These are enough for the spir-v generator to handle UConvert
and SConvert operations, and fix the 4 tests in CTS.

Reviewed-by: Samuel Iglesias Gonsálvez <b753b212f30aed827c3eea2e437609dc37310153@igalia.com>
Signed-off-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler