drm/i915: Remove I915_USER_PRIORITY_SHIFT

As we do not have any internal priority levels, the priority can be set
directed from the user values.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210120121439.17600-2-chris@chris-wilson.co.uk


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>