drm: Remove __OS_HAS_AGP

We already express the drm/agp depencies correctly in Kconfig, so we
can rip this remnant from the shared drm core days.

Aside: Pretty much all the #ifdefs in radeon/nouveau could be killed
if ttm would provide dummy functions. I'm not going to volunteer for
that though.

v2: Use IS_ENABLED(CONFIG_AGP) as suggested by Ville

v3: Polish from Ville's review.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com> (v2)
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/drm_memory.c b/drivers/gpu/drm/drm_memory.c
index a521ef6..87a8cb7 100644
--- a/drivers/gpu/drm/drm_memory.c
+++ b/drivers/gpu/drm/drm_memory.c
@@ -38,7 +38,7 @@
 #include <drm/drmP.h>
 #include "drm_legacy.h"
 
-#if __OS_HAS_AGP
+#if IS_ENABLED(CONFIG_AGP)
 
 #ifdef HAVE_PAGE_AGP
 # include <asm/agp.h>
@@ -111,14 +111,14 @@
 	return agp_unbind_memory(handle);
 }
 
-#else  /*  __OS_HAS_AGP  */
+#else /*  CONFIG_AGP  */
 static inline void *agp_remap(unsigned long offset, unsigned long size,
 			      struct drm_device * dev)
 {
 	return NULL;
 }
 
-#endif				/* agp */
+#endif /* CONFIG_AGP */
 
 void drm_legacy_ioremap(struct drm_local_map *map, struct drm_device *dev)
 {