drivers/staging: make android ion_page_pool.c explicitly non-modular

The Kconfig currently controlling compilation of this code is:

drivers/staging/android/ion/Kconfig:menuconfig ION
drivers/staging/android/ion/Kconfig:    bool "Ion Memory Manager"

...meaning that it currently is not being built as a module by anyone.

Lets remove the modular code that is essentially orphaned, so that
when reading the driver there is no doubt it is builtin-only.

Since module_init translates to device_initcall in the non-modular
case, the init ordering remains unchanged with this commit.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Arve Hjønnevåg" <arve@android.com>
Cc: Riley Andrews <riandrews@android.com>
Cc: devel@driverdev.osuosl.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion_page_pool.c

@@ -19,7 +19,7 @@
 #include <linux/err.h>
 #include <linux/fs.h>
 #include <linux/list.h>
-#include <linux/module.h>
+#include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/swap.h>
 #include "ion_priv.h"
@@ -174,10 +174,4 @@ static int __init ion_page_pool_init(void)
 {
 	return 0;
 }
-
-static void __exit ion_page_pool_exit(void)
-{
-}
-
-module_init(ion_page_pool_init);
-module_exit(ion_page_pool_exit);
+device_initcall(ion_page_pool_init);