drm/i915/icl: Store available engine masks in INTEL_INFO

Upcoming GuC code will need to read the fused off engine masks as well,
and will also want to have them as enabled instead of disabled masks.

To consolidate the read-out place we can store them in this fashion inside
INTEL_INFO so they can be easily referenced in the future.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181018104106.30147-1-tvrtko.ursulin@linux.intel.com