sh, landisk: set HZ=64 again

sh, landisk: set HZ=64 again

The addition of HZ to sys/kernel.h in v1.26 overrides the default
definition of HZ in sh/clock.c, changing landisk from HZ=64 to HZ=100.

Explicitly set HZ=64 in the GENERIC and RAMDISK config(8) files to can
change it from 100 back to 64.

Not sure if this is the best thing, but it does fix the problem.

Problem confirmed by, and fix tested by, miod@.

ok miod@