radeonsi: unify CP DMA code determining various flags
radeonsi: unify CP DMA code determining various flags

v2: don't call get_flush_flags twice per function

Reviewed-by: Michel Dänzer <242b79f0804cf52679d58f27ed754158c1323c75@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler