drm/i915: Remove unused intel_flush_status_page()

intel_flush_status_page() is defunct since commit f8dd2934
("drm/i915: Remove BXT incoherent seqno write workaround"), time to
remove it.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170324163540.31981-2-chris@chris-wilson.co.ukReviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -438,14 +438,6 @@ intel_engine_flag(const struct intel_engine_cs *engine)
 	return 1 << engine->id;
 }
 
-static inline void
-intel_flush_status_page(struct intel_engine_cs *engine, int reg)
-{
-	mb();
-	clflush(&engine->status_page.page_addr[reg]);
-	mb();
-}
-
 static inline u32
 intel_read_status_page(struct intel_engine_cs *engine, int reg)
 {