drm/i915/dp: Silence compiler for missing prototype

drivers/gpu/drm/i915/intel_dp.c:3063:6: warning: no previous prototype for ‘intel_dp_get_alpm_status’ [-Wmissing-prototypes]
 bool intel_dp_get_alpm_status(struct intel_dp *intel_dp)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170114105113.1231-2-chris@chris-wilson.co.uk


Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>