gpio: mxc: Only get the second IRQ when there is more than one IRQ

On some of i.MX SoCs like i.MX8QXP, there is ONLY one IRQ for each
GPIO bank, so it is better to check the IRQ count before getting
second IRQ to avoid below error message during probe:

[    1.070908] gpio-mxc 5d080000.gpio: IRQ index 1 not found
[    1.077420] gpio-mxc 5d090000.gpio: IRQ index 1 not found
[    1.083766] gpio-mxc 5d0a0000.gpio: IRQ index 1 not found
[    1.090122] gpio-mxc 5d0b0000.gpio: IRQ index 1 not found
[    1.096470] gpio-mxc 5d0c0000.gpio: IRQ index 1 not found
[    1.102804] gpio-mxc 5d0d0000.gpio: IRQ index 1 not found
[    1.109144] gpio-mxc 5d0e0000.gpio: IRQ index 1 not found
[    1.115475] gpio-mxc 5d0f0000.gpio: IRQ index 1 not found

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>