clk: sunxi: Let divs clocks read the base factor clock name from devicetree

Currently, the sunxi clock driver gets the name for the base factor clock
of divs clocks from the name field in factors_data. This prevents reusing
of the factor clock for clocks with same properties, but different name.

This commit makes the divs setup function try to get a name from
clock-output-names in the devicetree. It also removes the name field where
possible and merges the sun4i PLL5 and PLL6 clocks.

[Andre: Make temporary name allocation dynamic.]

Signed-off-by: Jens Kuske <jenskuske@gmail.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>