Revert "drm/i915/icl: WaEnableFloatBlendOptimization"

The register for 0xe420 is unable to hold any value, including
this bit. The documentation is also mixed between having a
register bit for toggle and having a state command setup
for it. Apparently the register toggle is deprecated.

Remove the register toggle as evidence shows it's futile.

The thing remaining is an apology and humble request for
Mesa folks to resurrect their state setup for this as they
were on right track from start.

This reverts commit 0bf059f3.

Fixes: 0bf059f3 ("drm/i915/icl: WaEnableFloatBlendOptimization")
References: HSDES#1406393558
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: Anuj Phogat <anuj.phogat@gmail.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Signed-off-by: NMika Kuoppala <mika.kuoppala@linux.intel.com>
Acked-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180730120636.26958-1-mika.kuoppala@linux.intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -2859,9 +2859,6 @@ enum i915_power_well_id {
 #define   GEN8_4x4_STC_OPTIMIZATION_DISABLE	(1 << 6)
 #define   GEN9_PARTIAL_RESOLVE_IN_VC_DISABLE	(1 << 1)
 
-#define GEN10_CACHE_MODE_SS			_MMIO(0xe420)
-#define   FLOAT_BLEND_OPTIMIZATION_ENABLE	(1 << 4)
-
 #define GEN6_BLITTER_ECOSKPD	_MMIO(0x221d0)
 #define   GEN6_BLITTER_LOCK_SHIFT			16
 #define   GEN6_BLITTER_FBC_NOTIFY			(1 << 3)

drivers/gpu/drm/i915/intel_workarounds.c

@@ -508,9 +508,6 @@ static int icl_ctx_workarounds_init(struct drm_i915_private *dev_priv)
 		WA_SET_BIT_MASKED(GEN11_COMMON_SLICE_CHICKEN3,
 				  GEN11_BLEND_EMB_FIX_DISABLE_IN_RCC);
 
-	/* WaEnableFloatBlendOptimization:icl */
-	WA_SET_BIT_MASKED(GEN10_CACHE_MODE_SS, FLOAT_BLEND_OPTIMIZATION_ENABLE);
-
 	return 0;
 }