clk: mvebu: ap806: Prepare the introduction of AP807 clock support

Factor out the code that is only useful to AP806 so it will be easier
to support AP807. No functional changes.

Signed-off-by: Ben Peled <bpeled@marvell.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lkml.kernel.org/r/20190805100310.29048-8-miquel.raynal@bootlin.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>