m68k: Reverse platform MMU logic so Sun 3 is last

m68k: Reverse platform MMU logic so Sun 3 is last

Currently Sun 3 support is the first platform option, as the Sun 3 MMU is
incompatible with standard Motorola MMUs. However, this means that
`allmodconfig' enables support for Sun 3, and thus disables support for all
other platforms.

Reverse the logic and move Sun 3 last, so `allmodconfig' enables all
platforms except for Sun 3, increasing compile-coverage.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>