Document USB phy bindings for RZ/G2L SoC.

RZ/G2L USB2.0 phy uses line ctrl register for OTG_ID pin changes. It uses
a different OTG-BC interrupt bit for device recognition. Apart from this,
the PHY reset is controlled by USBPHY control IP and Document reset is a
required property.
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210727185527.19907-3-biju.das.jz@bp.renesas.comSigned-off-by: Vinod Koul <vkoul@kernel.org>