pinctrl: mvebu: armada-37xx: use use platform api

pinctrl: mvebu: armada-37xx: use use platform api

platform_irq_count() and platform_get_irq() is the more generic
way (independent of device trees) to determine the count of available
interrupts. So use this instead.

As platform_irq_count() might return an error code (which
of_irq_count doesn't) some additional handling is necessary.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/1576672860-14420-1-git-send-email-peng.fan@nxp.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>