Marvell/Library: ArmadaSoCDescLib/MppLib: Extend Xenon information

Hitherto SoC description and MppLib libraries code assumed
that there could be only two Xenon SdMmc controller
instances in the SoC. Remove those limitations, so that
to support CN913x SoCs, which may have up to 4 of such interfaces.

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