m68k/mac: Use '030 reset method on SE/30

The comment says that calling the ROM routine doesn't work. But testing
shows that the 68030 fall-back reset method does work, so just use that.

Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>