drm/i915: Inline gen6_sanitize_rps_pm_mask()

gen6_sanitize_rps_pm_mask() is small enough that inlining it shrinks the
object code.

v2: Use const markup

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170312135426.2216-1-chris@chris-wilson.co.uk


Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>