staging/comedi: Move comedi_pci_auto_unconfig to drivers.c

Since comedi_pci_auto_unconfig cannot be inlined anymore after
 staging/comedi: Use comedi_pci_auto_unconfig directly for
 pci_driver.remove
is applied, it makes sense to move it drivers.c

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>