[IDE] Add driver for Sibyte Swarm evaluation board

This driver supports the IDE port on the Sibyte Swarm evaluation boards
and it's relatives for the BCM1250 family of systems on a chip.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Acked-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>