arm64: dts: r8a7795: salvator-x: add bias setting for usb1_pins

Since this board doesn't mount pull-up/down registers for
USB1_{OVC,PWEN} pins, we should enable bias setting to pull these
pins up/down.

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