drm/i915: Move the context descriptor to an inline helper

The context descriptor is stored inside the per-engine context state, as
we only need to compute it once and access it frequently. However,
currently only intel_lrc.c has easy access, but i915_guc_submission.c
would like to frequently read it as well, and more so only ever needs
the lower 32bits. Make it an inline as the compiler should be able to
retrieve the value in less instructions than it takes to do the function
call:

add/remove: 0/1 grow/shrink: 1/0 up/down: 8/-45 (-37)
function                                     old     new   delta
i915_guc_submit                              621     629      +8
intel_lr_context_descriptor                   45       -     -45

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20170912214905.21987-1-chris@chris-wilson.co.uk
Reviewed-by: Oscar Mateo <oscar.mateo@intel.com>

drivers/gpu/drm/i915/intel_lrc.c

@@ -286,12 +286,6 @@ intel_lr_context_descriptor_update(struct i915_gem_context *ctx,
 	ce->lrc_desc = desc;
 }
 
-uint64_t intel_lr_context_descriptor(struct i915_gem_context *ctx,
-				     struct intel_engine_cs *engine)
-{
-	return ctx->engine[engine->id].lrc_desc;
-}
-
 static inline void
 execlists_context_status_change(struct drm_i915_gem_request *rq,
 				unsigned long status)

drivers/gpu/drm/i915/intel_lrc.h

@@ -25,6 +25,7 @@
 #define _INTEL_LRC_H_
 
 #include "intel_ringbuffer.h"
+#include "i915_gem_context.h"
 
 #define GEN8_LR_CONTEXT_ALIGN I915_GTT_MIN_ALIGNMENT
 
@@ -78,8 +79,14 @@ struct drm_i915_private;
 struct i915_gem_context;
 
 void intel_lr_context_resume(struct drm_i915_private *dev_priv);
-uint64_t intel_lr_context_descriptor(struct i915_gem_context *ctx,
-				     struct intel_engine_cs *engine);
+
+static inline uint64_t
+intel_lr_context_descriptor(struct i915_gem_context *ctx,
+			    struct intel_engine_cs *engine)
+{
+	return ctx->engine[engine->id].lrc_desc;
+}
+
 
 /* Execlists */
 int intel_sanitize_enable_execlists(struct drm_i915_private *dev_priv,