UniCore32 bugfix: add missed CONFIG_ZONE_DMA

Because our PCI-bus handler confines dma zone into 128M, we should add
CONFIG_ZONE_DMA for all boards. Otherwise, all memory bigger than 128M
will be pushed into ZONE_MOVABLE.

Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Liu Guoli <liuguoli@mprc.pku.edu.cn>
Signed-off-by: Guan Xuetao <gxt@mprc.pku.edu.cn>