m68knommu: fix non-specific 68328 choice interrupt build failure

Compiling for a classic m68k non-MMU target with no specific CPU
selected fails with the following error:

   arch/m68k/68000/ints.c: In function 'process_int':
>> arch/m68k/68000/ints.c:82:30: error: 'ISR' undeclared (first use in this function)
      82 |         unsigned long pend = ISR;
         |                              ^~~

This interrupt handling code is specific to the 68328 family of 68000
parts. There is a couple of variants (68EZ328, 68VZ328) and the common
ancestor of them the strait 68328.

The code here includes a specific header for each variant type. But if
none is selected then nothing is included to supply the appropriate
register and bit flags defines.

Rearrange the includes so that at least one type is always included.
At the very least the 68328 base type should be the fallback, so make
that true.

Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>