gpio: omap: do not register driver in probe()

In the Linux kernel, the following vulnerability has been resolved:

gpio: omap: do not register driver in probe()

Commit 11a78b794496 ("ARM: OMAP: MPUIO wake updates") registers the

omap_mpuio_driver from omap_mpuio_init(), which is called from

omap_gpio_probe().

However, it neither makes sense to register drivers from probe()

callbacks of other drivers, nor does the driver core allow registering

drivers with a device lock already being held.

The latter was revealed by commit dc23806a7c47 ("driver core: enforce

device_lock for driver_match_device()") leading to a potential deadlock

condition described in [1].

Additionally, the omap_mpuio_driver is never unregistered from the

driver core, even if the module is unloaded.

Hence, register the omap_mpuio_driver from the module initcall and

unregister it in module_exit().