[ARM] add Marvell Kirkwood (88F6000) SoC support

The Marvell Kirkwood (88F6000) is a family of ARM SoCs based on a
Shiva CPU core, and features a DDR2 controller, a x1 PCIe interface,
a USB 2.0 interface, a SPI controller, a crypto accelerator, a TS
interface, and IDMA/XOR engines, and depending on the model, also
features one or two Gigabit Ethernet interfaces, two SATA II
interfaces, one or two TWSI interfaces, one or two UARTs, a
TDM/SLIC interface, a NAND controller, an I2S/SPDIF interface, and
an SDIO interface.

This patch adds supports for the Marvell DB-88F6281-BP Development
Board and the RD-88F6192-NAS and the RD-88F6281 Reference Designs,
enabling support for the PCIe interface, the USB interface, the
ethernet interfaces, the SATA interfaces, the TWSI interfaces, the
UARTs, and the NAND controller.

Signed-off-by: Saeed Bishara <saeed@marvell.com>
Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>