phy: renesas: rcar-gen3-usb2: Check a property to use otg pins

Since All R-Car Gen3 SoCs have dedicated otg pins actually but
some boards don't use the otg pins (e.g. R-Car D3 Draak and R-Car E3
Ebisu), the driver should not choose SoC model base by using
rcar_gen3_phy_usb2_match_table's data. So, this patch checks a
"renesas,no-otg-pins" property to set the "uses_otg_pins".

Note that since r8a77995-draak.dts and r8a77990-ebisu.dts don't have
'dr_mode = "otg";' for now, if we apply this patch, no behavior
changes (the value of "uses_otg_pins" is false).

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>