drm/i915: Unify CHICKEN_PIPESL_1 register definitions

We have two names for the same register CHICKEN_PIPESL_1 and
HSW_PIPE_SLICE_CHICKEN_1. Unify it to just one.

Also rename the FBCQ disable bit to resemble the name we've
given to a similar bit on earlier platforms.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>