usb: hide unused usbfs_notify_suspend/resume functions

usb: hide unused usbfs_notify_suspend/resume functions

The declaration is in an #ifdef, which causes warnings when building
with 'make W=1' and without CONFIG_PM:

drivers/usb/core/devio.c:742:6: error: no previous prototype for 'usbfs_notify_suspend'
drivers/usb/core/devio.c:747:6: error: no previous prototype for 'usbfs_notify_resume'

Use the same #ifdef check around the function definitions to avoid
the warnings and slightly shrink the USB core.

Fixes: 7794f486ed0b ("usbfs: Add ioctls for runtime power management")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20230516202103.558301-1-arnd@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>