drm/i915: Decrease number of subplatform bits

Commit 6ce1c33d ("drm/i915: Kill INTEL_SUBPLATFORM_AML") removed the
only platform which used bit 2 so could also decrease the
INTEL_SUBPLATFORM_BITS definition.

This is not a fixes material but still lets make it precise.

v2:
 * Fix assert in intel_device_info_subplatform_init by introducing
   INTEL_SUBPLATFORM_MASK. (Chris)
 * Update intel_subplatform().
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
References: 6ce1c33d ("drm/i915: Kill INTEL_SUBPLATFORM_AML")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
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/20210121161936.746591-2-tvrtko.ursulin@linux.intel.comSigned-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1298,7 +1298,7 @@ intel_subplatform(const struct intel_runtime_info *info, enum intel_platform p)
 {
 	const unsigned int pi = __platform_mask_index(info, p);
 
-	return info->platform_mask[pi] & ((1 << INTEL_SUBPLATFORM_BITS) - 1);
+	return info->platform_mask[pi] & INTEL_SUBPLATFORM_MASK;
 }
 
 static __always_inline bool

drivers/gpu/drm/i915/intel_device_info.c

@@ -223,7 +223,7 @@ void intel_device_info_subplatform_init(struct drm_i915_private *i915)
 		}
 	}
 
-	GEM_BUG_ON(mask & ~INTEL_SUBPLATFORM_BITS);
+	GEM_BUG_ON(mask & ~INTEL_SUBPLATFORM_MASK);
 
 	RUNTIME_INFO(i915)->platform_mask[pi] |= mask;
 }

drivers/gpu/drm/i915/intel_device_info.h

@@ -93,7 +93,8 @@ enum intel_platform {
  * it is fine for the same bit to be used on multiple parent platforms.
  */
 
-#define INTEL_SUBPLATFORM_BITS (3)
+#define INTEL_SUBPLATFORM_BITS (2)
+#define INTEL_SUBPLATFORM_MASK (BIT(INTEL_SUBPLATFORM_BITS) - 1)
 
 /* HSW/BDW/SKL/KBL/CFL */
 #define INTEL_SUBPLATFORM_ULT	(0)