drm/i915: Remove BXT disable pixel mask clamping w/a

This w/a (WaSetDisablePixMaskCammingAndRhwoInCommonSliceChicken) was only
used for preproduction hw, which is no longer in use. Remove the
workaround to simplify the code.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170123130601.2281-4-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/intel_lrc.c

@@ -1170,15 +1170,6 @@ static int gen9_init_perctx_bb(struct intel_engine_cs *engine,
 {
 	uint32_t index = wa_ctx_start(wa_ctx, *offset, CACHELINE_DWORDS);
 
-	/* WaSetDisablePixMaskCammingAndRhwoInCommonSliceChicken:bxt */
-	if (IS_BXT_REVID(engine->i915, 0, BXT_REVID_A1)) {
-		wa_ctx_emit(batch, index, MI_LOAD_REGISTER_IMM(1));
-		wa_ctx_emit_reg(batch, index, GEN9_SLICE_COMMON_ECO_CHICKEN0);
-		wa_ctx_emit(batch, index,
-			    _MASKED_BIT_ENABLE(DISABLE_PIXEL_MASK_CAMMING));
-		wa_ctx_emit(batch, index, MI_NOOP);
-	}
-
 	/* WaClearTdlStateAckDirtyBits:bxt */
 	if (IS_BXT_REVID(engine->i915, 0, BXT_REVID_B0)) {
 		wa_ctx_emit(batch, index, MI_LOAD_REGISTER_IMM(4));