radeonsi: accept pipe_resource in si_sampler_view_add_buffer
radeonsi: accept pipe_resource in si_sampler_view_add_buffer

and rename .._buffers -> .._buffer

Based loosely on Nicolai's patch. This will make it easier to cherry-pick
Nicolai's patches from his image support branch.

Reviewed-by: Michel Dänzer <242b79f0804cf52679d58f27ed754158c1323c75@amd.com>
Reviewed-by: Nicolai Hähnle <0d0be6cf5ad662651be2dc5dfd44aa2b09d4c1cc@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler