arm: dts: rockchip: remove usb-phy fallback string for rk3188

arm: dts: rockchip: remove usb-phy fallback string for rk3188

With the conversion of rockchip-usb-phy.yaml a long time used fallback
string for rk3066a/rk3188 was added. The linux driver doesn't do much with
the GRF phy address range, however the u-boot driver rockchip_usb2_phy.c
does. The bits in GRF_UOC0_CON2 for rk3066a/rk3188 and rk3288 for example
don't match. Remove the usb-phy fallback string for rk3188
to prevent possible strange side effects.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>