When USB is disabled, we get a link error for this driver
because of the added OTG support

drivers/phy/renesas/phy-rcar-gen3-usb2.o: In function `rcar_gen3_phy_usb2_probe':
phy-rcar-gen3-usb2.c:(.text+0x250): undefined reference to `of_usb_get_dr_mode_by_phy'

Other phy drivers select USB_COMMON for this, so let's do the same
here.

Fixes: 7e0540f4 ("phy: rcar-gen3-usb2: check dr_mode for otg mode")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>