staging: comedi: amplc_pc236: split into ISA, PCI and common module

The "amplc_pc236" driver currently handles both ISA and PCI devices and
uses a small amount of conditional compilation depending which are
enabled.

Move most of the functionality into a new module, "amplc_pc236_common",
and split off support for PCI devices into a new module, "amplc_pci236".
Retain support for ISA devices in the existing module, "amplc_pc236".

Since the `detach` handler (`pc236_detach()`) in the existing module
"amplc_pc236" now only needs to handle ISA devices and only calls
`comedi_legacy_detach()`, just use `comedi_legacy_detach()` directly as
the `detach` handler in `struct comedi_driver amplc_pc236_driver`.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>