Documentation/i915: Fix kernel-doc references to moved gem files

The error messages could be more descriptive, but fix these caused by
file moves:

WARNING: kernel-doc './scripts/kernel-doc -rst -enable-lineno -internal
    ./drivers/gpu/drm/i915/i915_gem_shrinker.c' failed with return code 2
WARNING: kernel-doc './scripts/kernel-doc -rst -enable-lineno -function
    User command execution ./drivers/gpu/drm/i915/i915_gem_execbuffer.c'
    failed with return code 1
WARNING: kernel-doc './scripts/kernel-doc -rst -enable-lineno -internal
    ./drivers/gpu/drm/i915/i915_gem_tiling.c' failed with return code 2
WARNING: kernel-doc './scripts/kernel-doc -rst -enable-lineno -function
    buffer object tiling ./drivers/gpu/drm/i915/i915_gem_tiling.c'
    failed with return code 1

Fixes: 10be98a7 ("drm/i915: Move more GEM objects under gem/")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190605095657.23601-1-jani.nikula@intel.com

Documentation/gpu/i915.rst

@@ -349,7 +349,7 @@ of buffer object caches. Shrinking is used to make main memory
 available. Note that this is mostly orthogonal to evicting buffer
 objects, which has the goal to make space in gpu virtual address spaces.
 
-.. kernel-doc:: drivers/gpu/drm/i915/i915_gem_shrinker.c
+.. kernel-doc:: drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
    :internal:
 
 Batchbuffer Parsing
@@ -373,7 +373,7 @@ Batchbuffer Pools
 User Batchbuffer Execution
 --------------------------
 
-.. kernel-doc:: drivers/gpu/drm/i915/i915_gem_execbuffer.c
+.. kernel-doc:: drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
    :doc: User command execution
 
 Logical Rings, Logical Ring Contexts and Execlists
@@ -382,9 +382,6 @@ Logical Rings, Logical Ring Contexts and Execlists
 .. kernel-doc:: drivers/gpu/drm/i915/gt/intel_lrc.c
    :doc: Logical Rings, Logical Ring Contexts and Execlists
 
-.. kernel-doc:: drivers/gpu/drm/i915/gt/intel_lrc.c
-   :internal:
-
 Global GTT views
 ----------------
 
@@ -415,10 +412,10 @@ Hardware Tiling and Swizzling Details
 Object Tiling IOCTLs
 --------------------
 
-.. kernel-doc:: drivers/gpu/drm/i915/i915_gem_tiling.c
+.. kernel-doc:: drivers/gpu/drm/i915/gem/i915_gem_tiling.c
    :internal:
 
-.. kernel-doc:: drivers/gpu/drm/i915/i915_gem_tiling.c
+.. kernel-doc:: drivers/gpu/drm/i915/gem/i915_gem_tiling.c
    :doc: buffer object tiling
 
 WOPCM