Improve interrupt and resource allocation in Marvell GPIO driver

This patch adds support for more than one interrupts
in GPIO controller. It reads necessary information (such as cell size)
from FDT, so there are no magic numbers.

Note that interrupts are still not working, but this patch makes
one good step in correct direction

Submitted by: Patryk Duda <pdk@semihalf.com>
Obtained from: Semihalf
Sponsored by: Stormshield
Differential Revision: https://reviews.freebsd.org/D14754