[PATCH RFC 0/2] Fix m68k multiplatform ISA support

[Michael Schmitz <schmitzmic@gmail.com>]

Finn Thain found out that our multiplatform support is broken when
attempting to build a kernel with support for both Q40 and Atari (when
setting CONFIG_ISA through CONFIG_Q40, but not CONFIG_ATARI_ROM_ISA).

Inspection of the code in io_mm.h reveals that in that case, ISA I/O
accessors with address translation are used for the Atari IDE driver, where
MMIO accessors with no address translation would have been appropriate.

Setting CONFIG_ATARI_ROM_ISA will fix the issue for Atari, but then force the
use of I/O accessors without address translation for Q40. The code in
io_mm.h is fundamentally broken for kernels that have both Q40 and Atari
support. 

Address this by adding a check for address < 1024 to the Atari address
translation case, changing the default address translation to return the
untranslated address, and changing the CONFIG_ATARI_ROM_ISA section to use
ISA I/O accessors for addresses > 1024 (i.e., those not intended to map to
the ROM port).

Tested on ARAnyM with all combinations of CONFIG_ATARI_ROM_ISA and
CONFIG_ISA. Earlier versions tested on my Falcon hardware, all using
pata_falcon. 

A thorough review in particular in regard to ramifications for Q40 and Amiga
would be welcome. If there is a better way to implement these changes, I'd
appreciate a hint. This is all academic as long as support for Q40 and Atari
in the same kernel image is not needed, of course. 

I suspect patch 2 may not be needed, since the isa_sex variable should always 
be zero? 

Cheers,

   Michael