drm/i915: take a reference to uncore in the engine and use it

A few advantages:

- Prepares us for the planned split of display uncore from GT uncore

- Improves our engine-centric view of the world in the engine code
  and allows us to avoid jumping back to dev_priv.

- Allows us to wrap accesses to engine register in nice macros that
  automatically pick the right mmio base.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190325214940.23632-10-daniele.ceraolospurio@intel.com
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 47bf07a..bb2c16c 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -880,7 +880,7 @@ static int i915_interrupt_info(struct seq_file *m, void *data)
 		for_each_engine(engine, dev_priv, id) {
 			seq_printf(m,
 				   "Graphics Interrupt mask (%s):	%08x\n",
-				   engine->name, I915_READ_IMR(engine));
+				   engine->name, ENGINE_READ(engine, RING_IMR));
 		}
 	}