rockchip: rk3328: enable DMA for MMCs at Rock64

DMA for MMCs can be enabled, since the previous patch fixes
the following issue in SPL:

    Trying to boot from MMC1
    spl: mmc init failed with error: -110
    SPL: failed to boot from all boot devices
    ### ERROR ### Please RESET the board ###

Signed-off-by: Matwey V. Kornilov <matwey.kornilov@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>