time: sh: convert to use arch_getoffset() infrastructure

Convert sh to use GENERIC_TIME via the arch_getoffset() infrastructure.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>