MFC r348880, r348882

r348880 by loos:
Add the GPIO driver for the North/South bridge in Marvell Armada 37x0.

The A3700 has a different GPIO controller and thus, do not use the old (and
shared) code for Marvell.

The pinctrl driver, also part of the controller, is not supported yet (but
the implementation should be straightforward).

Sponsored by: Rubicon Communications, LLC (Netgate)

r348882 by loos:
Add support for the GPIO SD Card VCC regulator/switch and the GPIO SD Card
detection pins to the Marvell Xenon SDHCI controller.

These features are enable by 'vqmmc-supply' and 'cd-gpios' properties in the
DTS.

This fixes the SD Card detection on espressobin.

Sponsored by: Rubicon Communications, LLC (Netgate)