drm/mgag200: fix include notation and remove -Iinclude/drm flag

Include <drm/*.h> instead of relative path from include/drm, then
remove the -Iinclude/drm compiler flag.

Signed-off-by: Masahiro Yamada <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/mgag200/Makefile

···
-ccflags-y := -Iinclude/drm
 mgag200-y   := mgag200_main.o mgag200_mode.o mgag200_cursor.o \
 	mgag200_drv.o mgag200_fb.o mgag200_i2c.o mgag200_ttm.o
 

drivers/gpu/drm/mgag200/mgag200_ttm.c

···
  * Authors: Dave Airlie <[e-mail]>
  */
 #include <drm/drmP.h>
+#include <drm/ttm/ttm_page_alloc.h>
+
 #include "mgag200_drv.h"
-#include <ttm/ttm_page_alloc.h>
 
 static inline struct mga_device *
 mgag200_bdev(struct ttm_bo_device *bd)