[WATCHDOG] max63xx driver depends on ioremap()

Correct fix for the "ioremap() causes build failure on S390" should have been
a dependancy on HAS_IOMEM. So we add this dependancy also (and leave the driver
in the ARM section for now).

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>