staging: comedi: mite.h: remove "../comedi_pci.h" and make self-reliant

"mite.h" relies on a lot of things declared including "../comedi_pci.h",
but doesn't need anything in "../comedi_pci.h" itself.  None of the
Comedi modules that include "mite.h" rely on it to include
"../comedi_pci.h" on their behalf.

Remove the inclusion of "../comedi_pci.h" from "mite.h", and add enough
other includes and (incomplete) `struct` declarations to make it compile
without warnings or errors even when included first in a .c file.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>