configs/cca-3world: Use CONFIG_HZ_100 for the kernel

Running the CCA guest on an emulated platform is very slow. An easy
optimization is reducing the number of context switches to the host due
to timer interrupts, since context switches are very expensive on CCA.
Using HZ_100 instead of the default HZ_250 improves guest boot time.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>