"drivers/staging: mark android/ion fcns with EXPORT_SYMBOL for tristate

"drivers/staging: mark android/ion fcns with EXPORT_SYMBOL for tristate

In a recent change, we made a bool into a tristate in:
"drivers/staging: make android tegra_ion.c properly tristate", since it
was self evident that was the original intention.  However on the final
link phase we'll see an allmodconfig fail with:

ERROR: "ion_device_add_heap" [drivers/staging/android/ion/tegra/tegra_ion.ko] undefined!
ERROR: "ion_heap_create" [drivers/staging/android/ion/tegra/tegra_ion.ko] undefined!
ERROR: "ion_device_create" [drivers/staging/android/ion/tegra/tegra_ion.ko] undefined!
ERROR: "ion_heap_destroy" [drivers/staging/android/ion/tegra/tegra_ion.ko] undefined!
ERROR: "ion_device_destroy" [drivers/staging/android/ion/tegra/tegra_ion.ko] undefined!

Export the above using the non GPL specific export, since that is what
the rest of the ion code base does.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Arve Hjønnevåg" <arve@android.com>
Cc: Riley Andrews <riandrews@android.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: Markus Elfring <elfring@users.sourceforge.net>
Cc: devel@driverdev.osuosl.org
Cc: linux-tegra@vger.kernel.org
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>