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_vm.c b/drivers/gpu/drm/drm_vm.c
index aab49ee..f90bd5f 100644
--- a/drivers/gpu/drm/drm_vm.c
+++ b/drivers/gpu/drm/drm_vm.c
@@ -95,7 +95,7 @@
  * Find the right map and if it's AGP memory find the real physical page to
  * map, get the page, increment the use count and return it.
  */
-#if __OS_HAS_AGP
+#if IS_ENABLED(CONFIG_AGP)
 static int drm_do_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
 	struct drm_file *priv = vma->vm_file->private_data;
@@ -168,12 +168,12 @@
 vm_fault_error:
 	return VM_FAULT_SIGBUS;	/* Disallow mremap */
 }
-#else				/* __OS_HAS_AGP */
+#else
 static int drm_do_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
 	return VM_FAULT_SIGBUS;
 }
-#endif				/* __OS_HAS_AGP */
+#endif
 
 /**
  * \c nopage method for shared virtual memory.
@@ -556,7 +556,7 @@
 	 * --BenH.
 	 */
 	if (!vma->vm_pgoff
-#if __OS_HAS_AGP
+#if IS_ENABLED(CONFIG_AGP)
 	    && (!dev->agp
 		|| dev->agp->agp_info.device->vendor != PCI_VENDOR_ID_APPLE)
 #endif