mmc: sdhci-pxav3: add support for the Armada 38x SDHCI controller

The SDHCI unit used on the Armada 380 and 385 Marvell SoC is similar
to the PXAv3 unit. The only difference is that on Armada 38x, the
PXAv3 unit accesses memory through MBus windows which must be
configured prior to using the device. Without this, DMA would not
work.

In order to achieve this, the sdhci-pxav3 driver is extended with an
additional compatible string "marvell,armada-380-sdhci". When this
compatible string is used, the MBus windows are initialized in a way
that is identical to what all other DMA-capable drivers for Marvell
EBU platforms do.

Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Chris Ball <chris@printf.net>