drm: Move legacy buffer structures to <drm/drm_legacy.h>

A few odd cases:
- mgag200 someho had a totally unused drm_dma_handle_t. Remove it.
- i915 still uses the legacy pci dma alloc api, so grows an include.

Everything else fairly standard.

v2: Include "drm_legacy.h" in drm.ko source files for consistency.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/include/drm/ati_pcigart.h b/include/drm/ati_pcigart.h
index da4bfcd..5765648 100644
--- a/include/drm/ati_pcigart.h
+++ b/include/drm/ati_pcigart.h
@@ -1,6 +1,8 @@
 #ifndef DRM_ATI_PCIGART_H
 #define DRM_ATI_PCIGART_H
 
+#include <drm/drm_legacy.h>
+
 /* location of GART table */
 #define DRM_ATI_GART_MAIN 1
 #define DRM_ATI_GART_FB   2