drm/i915: Clarify uncore.lock locking

Only one place looked in need of a bit of polish: hsw_restore_lcpll.
It's used by the runtime pm code and hence is always called from
process context. No irq flag saving required.

Another thing I've stumbled over is that we might need to add a
raw forcewake_get/put helpers which don't grab a runtime pm reference
but just check that the device isn't suspended - we have this duplicated
in the execlist code, too.

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>