phy: renesas: rcar-gen3-usb2: follow the hardware manual procedure

This patch modifies rcar_gen3_init_otg() procedure to follow Figure
73.4 of "R-Car Series, 3rd Generation User's Manual: Hardware Rev.1.00".

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>