arm64: dts: renesas: salvator-common: add dr_mode property for USB2.0 channel 0

Since Salvator-X[S] have a USB2.0 dual-role channel (CN9), this patch
adds dr_mode property for USB2.0 channel 0 (EHCI/OHCI and HS-USB)
as "otg".

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>