drm/i915: Remove WA_(SET|CLR)_BIT

drm/i915: Remove WA_(SET|CLR)_BIT

These macros are of dubious merit when coupled with the per-context w/a
set. Instead of tweaking the value in the context, they tweak the value
based on the mmio at the time of recording; they are almost by
definition not per-context! Having removed the last users, remove the
macros to avoid temptation in the future.

v2: Kill WA_WRITE as well (now also unused).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171004124153.14142-2-chris@chris-wilson.co.uk
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>