usb: Add support for ACPI identification to xhci-platform

Provide the methods to let ACPI identify the need to use
xhci-platform. Change the Kconfig files so the
xhci-plat.o file is selectable during kernel config.

This has been tested on an ARM64 machine with platform XHCI, an
x86_64 machine with XHCI, and an x86_64 machine without XHCI.
There were no regressions or error messages on the machines
without platform XHCI.

[dhdang: regenerate the patch over v4.3-rc1 and address new comments]
Signed-off-by: Mark Langsdorf <mlangsdo@redhat.com>
Signed-off-by: Duc Dang <dhdang@apm.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>