ARM: rockchip: enable ZONE_DMA for non 64-bit capable peripherals

Most IP cores on ARM Rockchip platforms can only address 32 bits of
physical memory for DMA. Thus ZONE_DMA should be enabled when LPAE
is activated.

Signed-off-by: Tao Huang <huangtao@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>