drm/i915: Don't sanitize has_decoupled_mmio if platform is not broxton

The check in __intel_uncore_early_sanitize() to disable decoupled mmio
would disable it for every platform that is not broxton. While that's
not a problem now since only broxton supports that, simply setting
.has_decoupled_mmio in a new platform's device info wouldn't suffice. So
avoid future confusion and change the workaround to only change the
value of has_decoupled_mmio for broxton.

v2: git add compile fix. (Ander)

Cc: Praveen Paneri <praveen.paneri@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1479993807-29353-1-git-send-email-ander.conselvan.de.oliveira@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -2579,6 +2579,7 @@ intel_info(const struct drm_i915_private *dev_priv)
 #define BXT_REVID_A0		0x0
 #define BXT_REVID_A1		0x1
 #define BXT_REVID_B0		0x3
+#define BXT_REVID_B_LAST	0x8
 #define BXT_REVID_C0		0x9
 
 #define IS_BXT_REVID(dev_priv, since, until) \

drivers/gpu/drm/i915/intel_uncore.c

@@ -421,8 +421,7 @@ static void __intel_uncore_early_sanitize(struct drm_i915_private *dev_priv,
 				   GT_FIFO_CTL_RC6_POLICY_STALL);
 	}
 
-	/* Enable Decoupled MMIO only on BXT C stepping onwards */
-	if (!IS_BXT_REVID(dev_priv, BXT_REVID_C0, REVID_FOREVER))
+	if (IS_BXT_REVID(dev_priv, 0, BXT_REVID_B_LAST))
 		info->has_decoupled_mmio = false;
 
 	intel_uncore_forcewake_reset(dev_priv, restore_forcewake);