drm: move AGP definitions harder

Move drm_agp_head to drm_agpsupport.h and drm_agp_mem into drm_legacy.h.
Unfortunately, drivers still heavily access drm_agp_head so we cannot
move it to drm_legacy.h. However, at least it's no longer visible in
drmP.h now (it's directly included from it, though).

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/drm_memory.c b/drivers/gpu/drm/drm_memory.c
index 00c67c0..7888dad 100644
--- a/drivers/gpu/drm/drm_memory.c
+++ b/drivers/gpu/drm/drm_memory.c
@@ -36,6 +36,7 @@
 #include <linux/highmem.h>
 #include <linux/export.h>
 #include <drm/drmP.h>
+#include "drm_legacy.h"
 
 #if __OS_HAS_AGP
 static void *agp_remap(unsigned long offset, unsigned long size,