clk: renesas: rcar-usb2-clock-sel: Add multiple clocks management

This hardware needs to enable clocks of both host and peripheral.
So, this patch adds multiple clocks management.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/1583304137-28482-4-git-send-email-yoshihiro.shimoda.uh@renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>