i965/gen9: Refactor msrt mcs initialization
i965/gen9: Refactor msrt mcs initialization

This will be re-used to initialize auxiliary buffers in lossless
compression case.

Signed-off-by: Topi Pohjolainen <749697f19798b7f640b17221fd283b903825f071@intel.com>
Reviewed-by: Ben Widawsky <cf148a1c890adeeb4308e9e093ed95f3d05c8318@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler