Marvell/Drivers: MvBoardDesc: Extend protocol with MDIO support

Introduce new callback that can provide information
about MDIO controllers to the Mdio driver.

Extend ArmadaBoardDescLib with new structure MV_BOARD_MDIO_DESC,
for holding board specific data.

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