DMA support for RBM33G (mt7621)

Hi everyone!
I have Mikrotik RBM33G and Neoway n720 LTE modem. Neoway GobiNet Driver uses DMA, which, as I understood, is not supported by kernel.
make kernel_menuconfig automatically sets CONFIG_HAS_DMA to "yes" and all functions in usb driver "think" that system has DMA, but in proc file /proc/dma is not found.
File target/linux/ramips/dts/mt7621.dtsi has some fields like gdma and hsdma and I don't know is it exactly what I need.
Kernel config has option like "DMA Engine" with MTK support but I don't know how can it help me.
I have very poor knowledge about DMA. Can anyone help me?

add in the .dts of Your hardware
add module (=y) kmod-dma-ralink and kmod-hsdma

&gdma {
    status = "okay";

&hsdma {
    status = "okay";

Thank you @nicefile for reply! I already did it yesterday. Drivers were loaded successfully but usb-driver didn't communicate with it. I don't know how to disable using DMA by USB