ppc: Fix compile error for boards with CONFIG_DDR_ECC

A bug was introduced by commit e94e460c6e8741f42dab6d8dd4b596ba5d9d79ae
which affected non-MPC83xx/85xx/86xx ppc boards which had CONFIG_DDR_ECC
defined and resulted in errors such as:

Configuring for canyonlands board...
fsl_dma.c:50:2: error: #error "Freescale DMA engine not supported on your
processor"
make[1]: *** No rule to make target `.depend', needed by `libdma.a'.  Stop.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>