MIPS: BCM47XX: make reboot more relaiable

The reboot on the BCM47XX SoCs is done, by setting the watchdog counter
to 1 and let it trigger a reboot, when it reaches 0. Some devices with
a BCM4705/BCM4785 SoC do not reboot when the counter is set to 1 and
decreased to 0 by the hardware. It looks like it works more reliable
when we set it to 3. As far as I understand the hardware, this should
not make any difference, but I do not have access to any documentation
for this SoC.
It is still not 100% reliable.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: zajec5@gmail.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7488/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>