mmc: dw_mmc-rockchip: Add missing private data for very old controllers

In the Linux kernel, the following vulnerability has been resolved:

mmc: dw_mmc-rockchip: Add missing private data for very old controllers

The really old controllers (rk2928, rk3066, rk3188) do not support UHS

speeds at all, and thus never handled phase data.

For that reason it never had a parse_dt callback and no driver private

data at all.

Commit ff6f0286c896 ("mmc: dw_mmc-rockchip: Add memory clock auto-gating

support") makes the private data sort of mandatory, because the init

function checks whether phases are configured internally or through the

clock controller.

This results in the old SoCs then experiencing NULL-pointer dereferences

when they try to access that private-data struct.

While we could have if (priv) conditionals in all places, it's way less

cluttery to just give the old types their private-data struct.