usb: host: xhci-plat: add support for the R-Car H3 xHCI controllers

The R-Car H3 has two xHCI controllers. This SoC is compatible with
R-Car Gen2 SoCs, however this SoC doesn't need some specific registers
setting, and need a new firmware.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>