drm/i915: include shmem_fs.h only where needed

Don't include shmem_fs.h in i915_drv.h, reducing the build dependencies.

Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/44eade17f7ba1480d67c584466eeea3553f31506.1644507885.git.jani.nikula@intel.com

drivers/gpu/drm/i915/gem/i915_gem_shmem.c

@@ -5,6 +5,7 @@
  */
 
 #include <linux/pagevec.h>
+#include <linux/shmem_fs.h>
 #include <linux/swap.h>
 
 #include <drm/drm_cache.h>

drivers/gpu/drm/i915/gem/i915_gem_ttm.c

@@ -3,6 +3,8 @@
  * Copyright © 2021 Intel Corporation
  */
 
+#include <linux/shmem_fs.h>
+
 #include <drm/ttm/ttm_bo_driver.h>
 #include <drm/ttm/ttm_placement.h>
 

drivers/gpu/drm/i915/i915_drv.h

@@ -46,7 +46,6 @@
 #include <linux/perf_event.h>
 #include <linux/pm_qos.h>
 #include <linux/dma-resv.h>
-#include <linux/shmem_fs.h>
 #include <linux/stackdepot.h>
 
 #include <drm/drm_gem.h>