drm: move the buddy allocator from i915 into common drm

Move the base i915 buddy allocator code into drm
- Move i915_buddy.h to include/drm
- Move i915_buddy.c to drm root folder
- Rename "i915" string with "drm" string wherever applicable
- Rename "I915" string with "DRM" string wherever applicable
- Fix header file dependencies
- Fix alignment issues
- add Makefile support for drm buddy
- export functions and write kerneldoc description
- Remove i915 selftest config check condition as buddy selftest
  will be moved to drm selftest folder

cleanup i915 buddy references in i915 driver module
and replace with drm buddy

v2:
  - include header file in alphabetical order(Thomas)
  - merged changes listed in the body section into a single patch
    to keep the build intact(Christian, Jani)

v3:
  - make drm buddy a separate module(Thomas, Christian)

Signed-off-by: Arunpravin <Arunpravin.PaneerSelvam@amd.com>

drivers/gpu/drm/Kconfig

@@ -197,6 +197,12 @@ config DRM_TTM
 	  GPU memory types. Will be enabled automatically if a device driver
 	  uses it.
 
+config DRM_BUDDY
+	tristate
+	depends on DRM
+	help
+	  A page based buddy allocator
+
 config DRM_VRAM_HELPER
 	tristate
 	depends on DRM

drivers/gpu/drm/Makefile

@@ -35,6 +35,8 @@ drm-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
 
 obj-$(CONFIG_DRM_DP_AUX_BUS) += drm_dp_aux_bus.o
 
+obj-$(CONFIG_DRM_BUDDY) += drm_buddy.o
+
 drm_vram_helper-y := drm_gem_vram_helper.o
 obj-$(CONFIG_DRM_VRAM_HELPER) += drm_vram_helper.o