ANDROID: GKI: Enable CONFIG_USB_XHCI_HCD

Almost all systems support the USB XHCI controller these days, so build
it into the kernel so that everyone can share the same codebase.

If platform-specific XHCI changes are needed, do it in a
platform-specific XHCI driver using the provided api for that.

Bug: 157965270
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I6e8b5d1fbcde86415f43d942aad0f828ab346928