get rid of separate multipage fault-in primitives

* the only remaining callers of "short" fault-ins are just as happy with generic
variants (both in lib/iov_iter.c); switch them to multipage variants, kill the
"short" ones
* rename the multipage variants to now available plain ones.
* get rid of compat macro defining iov_iter_fault_in_multipage_readable by
expanding it in its only user.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/gpu/drm/armada/armada_gem.c

@@ -387,7 +387,7 @@ int armada_gem_pwrite_ioctl(struct drm_device *dev, void *data,
 	if (!access_ok(VERIFY_READ, ptr, args->size))
 		return -EFAULT;
 
-	ret = fault_in_multipages_readable(ptr, args->size);
+	ret = fault_in_pages_readable(ptr, args->size);
 	if (ret)
 		return ret;