staging: comedi: export alloc_subdevices as comedi_alloc_subdevices

Move the inline alloc_subdevices() function from comedidev.h
to drivers.c and rename it to comedi_alloc_subdevices(). The
function is large enough to warrant being an exported symbol
rather than being an inline in every driver.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>