xhci: split out rcar/rz support from xhci-plat.c

xhci: split out rcar/rz support from xhci-plat.c

The USB_XHCI_RZV2M and USB_RENESAS_USB3 select other drivers
based on the enabled SoC types, which leads to build failures
when the dependencies are not met:

WARNING: unmet direct dependencies detected for USB_RZV2M_USB3DRD
  Depends on [n]: USB_SUPPORT [=y] && USB_GADGET [=n] && (ARCH_R9A09G011 [=n] || COMPILE_TEST [=y])
  Selected by [m]:
  - USB_XHCI_RZV2M [=m] && USB_SUPPORT [=y] && USB [=y] && USB_XHCI_HCD [=m] && USB_XHCI_PLATFORM [=m] && (ARCH_R9A09G011 [=n] || COMPILE_TEST [=y])
ERROR: modpost: "rzv2m_usb3drd_reset" [drivers/usb/host/xhci-plat-hcd.ko] undefined!

The xhci-rcar driver has a reverse dependency with the xhci core, and it
depends on the UDC driver in turn. To untangle this, make the xhci-rcar.ko
driver a standalone module that just calls into the xhci-plat.ko module
like other drivers do.

This allows handling the dependency on the USB_RZV2M_USB3DRD driver to
only affect the xhci-rcar module and simplify the xhci-plat module.

It also allows leaving out the hacks for broken dma mask and nested
devices from the rcar side and keep that only in the generic xhci driver.

As a future cleanup, the marvell and dwc3 specific bits of xhci-plat.c
could be moved out as well, but that is not required for this bugfix.

Fixes: c52c9acc415e ("xhci: host: Add Renesas RZ/V2M SoC support")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20230131150531.12347-1-arnd@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>