Marvell/Cn9131Db: Introduce board support

This patch introduces all necessary components required
for building EDK2 firmware for CN9131-DB setup A.

In order to build this variant, '-D CN9131' flag should be added.

Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>