radv: fetch sample index via fmask for image coord as well.
radv: fetch sample index via fmask for image coord as well.

This follows the txf_ms code, I can't figure out why amdgpu-pro
doesn't do this in their shaders, they must know someone we don't.

This fixes:
dEQP-VK.pipeline.multisample_shader_builtin.sample_id.*

Reviewed-by: Bas Nieuwenhuizen <1d31d94f30d40df7951505d1034e1e923d02ec49@basnieuwenhuizen.nl>
Signed-off-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler