drm/i915: Save/restore irq state for vlv_residency_raw()

drm/i915: Save/restore irq state for vlv_residency_raw()

Since commit 6060b6aec03c ("drm/i915/pmu: Add RC6 residency metrics"),
vlv_residency_raw() may be called from an irq-disabled context (via perf
event sampling on remote cpu). As such, we can no longer assume that we
are called from process context and must save/restore the irq state for
the spinlock.

Fixes: 6060b6aec03c ("drm/i915/pmu: Add RC6 residency metrics")
Testcase: igt/perf_pmu/other-init-3
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20171122222510.22627-1-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>