drm/i915: Convert gt workarounds to intel_gt

More conversion of i915_gem_init_hw to uncore.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190621070811.7006-10-tvrtko.ursulin@linux.intel.com