gpio: mxc: fix race between chained IRQ handler install and probe completion

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

gpio: mxc: fix race between chained IRQ handler install and probe completion

mxc_update_irq_chained_handler() is called before the IRQ domain, the
generic IRQ chip, and the port list entry are set up. If an interrupt
arrives in that window:

- mx3_gpio_irq_handler() calls generic_handle_domain_irq() with
port->domain still NULL.
- mx2_gpio_irq_handler() walks mxc_gpio_ports, but the port has not
been added to the list yet.

Additionally, if any of the subsequent probe steps
(gpio_generic_chip_init(), devm_gpiochip_add_data(),
irq_domain_create_legacy(), or mxc_gpio_init_gc()) fail, the error
paths never unregister the chained handler, leaving a dangling handler
that points at freed memory.

Move the handler installation after all its dependencies are ready and
after list_add_tail(), so the handler is never live while the data
structures it touches are incomplete, and is never installed if probe
fails.