powerpc/83xx: add mpc8308_p1m DMA controller device-tree node

MPC8308 has DMA controller compatible with mpc512x_dma driver. This
patch adds device-tree node to support DMA controller on MPC8308 P1M
board.

Signed-off-by: Ilya Yanok <yanok@emcraft.com>
Acked-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>