pinctrl: nomadik: rename secondary to latent

The "secondary irq" in the nomadik pin control driver is actually
not secondary (as in: can occur any time alongside the ordinary
irq), it is a latent IRQ. It is an IRQ that has occurred when
the system was in sleep state and has been cached in a special
register flagged from the low power management unit (PRCM).

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>