drm/i915/icl: Fix VEBOX mismatch BUG_ON()

GT VEBOX DISABLE is only 4 bits wide but it was using a 8 bits wide
mask, the remaning reserved bits is set to 0 causing 4 more
nonexistent VEBOX engines being detected as enabled, triggering the
BUG_ON() because of mismatch between vebox_mask and newly added
VEBOX_MASK().

[   64.081621] [drm:intel_device_info_init_mmio [i915]] vdbox enable: 0005, instances: 0005
[   64.081763] [drm:intel_device_info_init_mmio [i915]] vebox enable: 00f1, instances: 0001
[   64.081825] intel_device_info_init_mmio:925 GEM_BUG_ON(vebox_mask != ({ unsigned int first__ = (VECS0); unsigned int count__ = (2); ((&(dev_priv)->__info)->engine_mask & (((~0UL) - (1UL << (first__)) + 1) & (~0UL >> (64 - 1 - (first__ + count__ - 1))))) >> first__; }))
[   64.082047] ------------[ cut here ]------------
[   64.082054] kernel BUG at drivers/gpu/drm/i915/intel_device_info.c:925!

BSpec: 20680
Fixes: 9511cb64 ("drm/i915: Adding missing '; ' to ENGINE_INSTANCES")
Fixes: 26376a7e ("drm/i915/icl: Check for fused-off VDBOX and VEBOX instances")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190326230223.26336-1-jose.souza@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -2953,7 +2953,7 @@ enum i915_power_well_id {
 #define GEN11_GT_VEBOX_VDBOX_DISABLE	_MMIO(0x9140)
 #define   GEN11_GT_VDBOX_DISABLE_MASK	0xff
 #define   GEN11_GT_VEBOX_DISABLE_SHIFT	16
-#define   GEN11_GT_VEBOX_DISABLE_MASK	(0xff << GEN11_GT_VEBOX_DISABLE_SHIFT)
+#define   GEN11_GT_VEBOX_DISABLE_MASK	(0x0f << GEN11_GT_VEBOX_DISABLE_SHIFT)
 
 #define GEN11_EU_DISABLE _MMIO(0x9134)
 #define GEN11_EU_DIS_MASK 0xFF