[ARM] orion5x: Fix soft-reset for some platforms

Some platforms, such as the DNS-323 rev C requires the soft reset line
to be toggled on and back off for the reset to work.

Note: The choice of 200ms delay comes from the 2.6.12 based vendor kernel.
It seems to be a -lot- though and I had my device working fine with much
smaller delays but better safe...

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Nicolas Pitre <nico@fluxnic.net>