Add the Marvell SDHCI controller to the list of supported devices in
sdhci_fdt.

Enable the SDHCI controller, bus and devices on ARMADA38X kernel.

Tested on: ClearFog Pro
Reviewed by: Marcin Wojtas <mw at semihalf.com>
Sponsored by: Rubicon Communications, LLC (Netgate)
Differential Revision: https://reviews.freebsd.org/D10606