sh: Always use CONFIG_HZ for HZ.

Currently the wdt forces HZ=1000 and sidesteps CONFIG_HZ completely. This
is a remnant from when HZ was hardcoded and before CONFIG_HZ was
introduced. Additionally, not all of the timers have this requirement
these days, so it's also an artificial limitation. Just kill it off and
use CONFIG_HZ directly.

Reported-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>