drm/i915: Move register white-listing to the common workaround framework

Instead of having a separate list of white-listed registers we can
trivially move this to the common workarounds framework.

This brings us one step closer to the goal of driving all workaround
classes using the same code.

v2:
 * Use GEM_DEBUG_WARN_ON for the sanity check. (Chris Wilson)

v3:
 * API rename. (Chris Wilson)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20181203125014.3219-6-tvrtko.ursulin@linux.intel.com