Introduce port debouncing mechanism in mv_gpio driver

This patch introduces gpio debouncing mechanism
with fixed memory allocation in critical section.

When you press button, value at gpio pin connected to button
is changing many times which will cause in unexpected behaviour.
Debouncing mechanism will prevent this phenomenon

Submitted by: Patryk Duda <pdk@semihalf.com>

	      Wojciech Macek <wma@semihalf.com>

Obtained from: Semihalf
Sponsored by: Stormshield
Differential Revision: https://reviews.freebsd.org/D14753