phy: rcar-gen3-usb2: add SoC-specific parameter for dedicated pins

This patch adds SoC-specific parameter to avoid reading/writing
specific registers wrongly if this driver runs on a SoC which doesn't
have dedicated pins (e.g. R-Car D3). This patch also changes the
value "has_otg" to "has_otg_pins" for slightly easier reading of
the code.

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>