Marvell/Library: ArmadaBoardDescLib: Add GPIO information

This patch extends library with GPIO devices per-board
description. Both embedded SoC controllers and
I2C IO expanders are supported. Add a helper routine
for obtaining information about the latter.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>