clk: bcm: rpi: Give firmware clocks a name

We've registered the firmware clocks using their ID as name, but it's much
more convenient to register them using their proper name. Since the
firmware doesn't provide it, we have to duplicate it.

Acked-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>