mips: bmips: add BCM6368 clock definitions

Add header with BCM6368 definitions in order to be able to include it from
device tree files.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Link: https://lore.kernel.org/r/20200615090231.2932696-7-noltari@gmail.com


Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>