Add dts file for ac14xx board and its board compatible
string to the generic mpc512x board match list.
Also add phandle to the dma DT node since there is a change
(for MPC5121 SDHC DMA support) merged via linux-mmc tree
with reference to the dma controller node in the sdhc node.
Signed-off-by: Anatolij Gustschin <agust@denx.de>