[ARM] add Marvell Loki (88RC8480) SoC support

The Marvell Loki (88RC8480) is an ARM SoC based on a Feroceon CPU
core running at between 400 MHz and 1.0 GHz, and features a 64 bit
DDR controller, 512K of internal SRAM, two x4 PCI-Express ports,
two Gigabit Ethernet ports, two 4x SAS/SATA controllers, two UARTs,
two TWSI controllers, and IDMA/XOR engines.

This patch adds support for the Marvell LB88RC8480 Development
Board, enabling the use of the PCIe interfaces, the ethernet
interfaces, the TWSI interfaces and the UARTs.

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