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

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>