MIPS: Alchemy: Wire up SD controller on DB/PB1200 boards.

Add au1xmmc platform data for PB1200/DB1200 boards and wire up the 2 SD
controllers for them.

Signed-off-by: Manuel Lauss <mano@roarinelk.homelinux.net>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>