firmware: raspberrypi: Move the clock IDs to the firmware header

We'll need the clock IDs in more drivers than just the clock driver from
now on, so let's move them in the firmware header.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>