dt-bindings: phy: Add Marvell COMPHY clocks

Marvell CP110 COMPHY block is fed by 3 clocks. Describe each of them in the
bindings.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>