Add GPIO support for QorIQ boards.

Add GPIO support for QorIQ boards.

This patch adds a GPIO controller support targeted for NXP LS1046A
SoC. The driver implements the following features:
 * setting direction of each pin (IN or OUT)
 * setting the mode of output pins (PUSHPULL or OPENDRAIN)
 * setting the state of each output pin (1 or 0)
 * reading the state of each input pin (1 or 0)

Submitted by: Kamil Koczurek <kek@semihalf.com>
              Dawid Gorecki <dgr@semihalf.com>
Reviewed by: manu
Obtained from: Semihalf
Sponsored by: Alstom Group
Differential Revision: https://reviews.freebsd.org/D24353