drm/i915: Unify request submission

Move request submission from emit_request into its own common vfunc
from i915_add_request().

v2: Convert I915_DISPATCH_flags to BIT(x) whilst passing
v3: Rename a few functions to match.
v4: Reenable execlists submission after disabling guc.
v5: Be aware that everyone calls i915_guc_submission_disable()!

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1469432687-22756-23-git-send-email-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470174640-18242-14-git-send-email-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index a885905..e378eb6 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -466,12 +466,9 @@
 	 */
 	request->postfix = ring->tail;
 
-	if (i915.enable_execlists)
-		ret = engine->emit_request(request);
-	else
-		ret = engine->add_request(request);
 	/* Not allowed to fail! */
-	WARN(ret, "emit|add_request failed: %d!\n", ret);
+	ret = engine->emit_request(request);
+	WARN(ret, "(%s)->emit_request failed: %d!\n", engine->name, ret);
 
 	/* Sanity check that the reserved size was large enough. */
 	ret = ring->tail - request_start;
@@ -483,6 +480,7 @@
 		  reserved_tail, ret);
 
 	i915_gem_mark_busy(engine);
+	engine->submit_request(request);
 }
 
 static unsigned long local_clock_us(unsigned int *cpu)