drm/i915: remove WA_SET_BIT_MASKED()

Just ommitting the list it's operating on doesn't save much typing and
adds another way to do the same thing. Just replace it with
wa_masked_en().

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20201205092542.2325477-2-lucas.demarchi@intel.com