MIPS: BCM63xx: Sync MIPS counters during CPU bringup

We are using the mips counters as the clock source, so we need to ensure
they are synced, else e.g. gettimeofday will return different values
depending on which core it was run.

Observed difference was about 8 seconds, causing ~8 seconds ping or time
running backwards for some programs.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: John Crispin <blogic@openwrt.org>
Cc: Maxime Bizon <mbizon@freebox.fr>
Cc: Florian Fainelli <florian@openwrt.org>
Cc: Kevin Cernekee <cernekee@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/7265/


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