Marvell/Armada7k8k: Introduce NonDiscoverable device init routines

To abstract the initialization required for non-discoverable devices,
which is often platform specific (e.g. enable GPIO-driven power supply),
introduce a NonDiscoverableInitLib for use by the NonDiscoverable code,
for which each platform can supply its own version.

Add XHCI power supply (so called 'VBUS') enabling routines
for supported platforms (Armada70x0Db, Armada80x0Db, Armada80x0McBin).

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