usb: gadget: udc: renesas_usb3: Add register of usb role switch

This patch adds role switch support for R-Car SoCs into the USB 3.0
peripheral driver. Some R-Car SoCs (e.g. R-Car H3) have USB 3.0
dual-role device controller which has the USB 3.0 xHCI host and
Renesas USB 3.0 peripheral.

Unfortunately, the mode change register (DRD_CON) contains
the USB 3.0 peripheral controller side only. So, this renesas_usb3
driver manages the DRD_CON now. However, in peripheral mode, the host
should stop. Also the host hardware needs to reinitialize its own
registers when the mode changes from peripheral to host mode.
Otherwise, the host cannot work correctly (e.g. detect a device
as high-speed).

To achieve this reinitialization by a driver, this driver also
registers a role switch driver to manage the DRD_CON and get
a device pointer of usb 3.0 host from "companion" property of OF.
Then, when the usb role is changed, renesas_usb3_role_switch_set()
will attach/release the xhci-plat driver to reinitialize the host
hardware.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>