r600: split out common alu_writes pattern.
r600: split out common alu_writes pattern.

This just splits out a common pattern into an inline function
to make things cleaner to read.

Reviewed-by: Glenn Kennard <feea5431f8695a3af7470d472cb16ac8e02bab01@gmail.com>
Signed-off-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler