Convert h8/300 to generic timekeeping

Currently h8/300 does not implement sub-jiffy timekeeping, so there is no
benefit to having arch specific timekeeping code.

This patch simply removes those functions and enables the generic
timekeeping code.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Acked-by: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>