anv/pipeline: Unconditionally emit PS_BLEND on gen8+
anv/pipeline: Unconditionally emit PS_BLEND on gen8+

Special-casing the PS_BLEND packet wasn't really gaining us anything.  It's
defined to be more-or-less the contents of blend state entry 0 only without
the indirection.  We can just copy-and-paste the contents.  If there are no
valid color targets, then blend state 0 will be 0-initialized anyway so
it's basically the same as the special case we had before.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler