drm/i915/gt: Use caller provided forcewake for intel_mocs_init_engine

During post-reset resume, we call intel_mocs_init_engine to reinitialise
the MOCS registers. Suprisingly, especially when enhanced by lockdep,
the acquisition of the forcewake lock around each register write takes a
substantial portion of the reset time. We don't need to use the
individual forcewake here as we can assume that the caller is holding a
blanket forcewake for the reset&resume and the resume is serialised.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190703155225.9501-2-chris@chris-wilson.co.uk