xen/apic/xenbus/swiotlb/pcifront/grant/tmem: Make functions or variables static.

There is no need for those functions/variables to be visible. Make them
static and also fix the compile warnings of this sort:

drivers/xen/<some file>.c: warning: symbol '<blah>' was not declared. Should it be static?

Some of them just require including the header file that
declares the functions.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
diff --git a/drivers/xen/xenbus/xenbus_dev_backend.c b/drivers/xen/xenbus/xenbus_dev_backend.c
index be738c4..d730008 100644
--- a/drivers/xen/xenbus/xenbus_dev_backend.c
+++ b/drivers/xen/xenbus/xenbus_dev_backend.c
@@ -107,7 +107,7 @@
 	return 0;
 }
 
-const struct file_operations xenbus_backend_fops = {
+static const struct file_operations xenbus_backend_fops = {
 	.open = xenbus_backend_open,
 	.mmap = xenbus_backend_mmap,
 	.unlocked_ioctl = xenbus_backend_ioctl,