dt-bindings: ap806: do not depend anymore of the *-clock-output-names

This patch updates the documentation according to the change made in the
patch "clk: mvebu: ap806: do not depend anymore of the
*-clock-output-names": the clock names are no more part of the binding.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/d502b5abc68cbb5739ce72ba8be27528f9042a28.1496239589.git-series.gregory.clement@free-electrons.com