usb/xhci: remove CONFIG_PCI in xhci.c's probe function

This removes the need of ifdefs within the init function and with it the
headache about the correct clean without bus X but with bus/platform Y &
Z.
xhci-pci is only compiled if CONFIG_PCI is selected which can be
de-selected now without trouble. For now the result is kinda useless
because we have no other glue code. However, since nobody is using
USB_ARCH_HAS_XHCI then it should not be an issue :)

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/host/xhci.h

@@ -1644,6 +1644,9 @@ void xhci_free_command(struct xhci_hcd *xhci,
 /* xHCI PCI glue */
 int xhci_register_pci(void);
 void xhci_unregister_pci(void);
+#else
+static inline int xhci_register_pci(void) { return 0; }
+static inline void xhci_unregister_pci(void) {}
 #endif
 
 /* xHCI host controller glue */