drm/i915/execlists: Simplify gen12_csb_parse

Having decided that we only care about the promotion predicate, we can
simplify gen12_csb_parse to simply check whether we need to jump to a
new queue.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190925130845.17952-1-chris@chris-wilson.co.uk