drm/amdgpu: Prepare DKMS build for powerplay module.

BugLink: http://bugs.launchpad.net/bugs/1546572Signed-off-by: Qiang Yu <Qiang.Yu@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>
(cherry picked from commit bd90dd89)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/gpu/drm/amd/amdgpu/Makefile

@@ -101,7 +101,7 @@ amdgpu-$(CONFIG_MMU_NOTIFIER) += amdgpu_mn.o
 
 ifneq ($(CONFIG_DRM_AMD_POWERPLAY),)
 
-include drivers/gpu/drm/amd/powerplay/Makefile
+include $(FULL_AMD_PATH)/powerplay/Makefile
 
 amdgpu-y += $(AMD_POWERPLAY_FILES)