clk: bcm: rpi: Split pllb clock hooks

clk: bcm: rpi: Split pllb clock hooks

The driver only supports the pllb for now and all the clock framework hooks
are a mix of the generic firmware interface and the specifics of the pllb.
Since we will support more clocks in the future let's split the generic and
specific hooks

Cc: Michael Turquette <mturquette@baylibre.com>
Cc: linux-clk@vger.kernel.org
Acked-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/fdc21962fdc7de5c46232f198672d5d5c868ec74.1592210452.git-series.maxime@cerno.tech
Signed-off-by: Stephen Boyd <sboyd@kernel.org>