dt-bindings: ap806: introduce a new binding

This patch updates the documentation according to the changes made in the
patch "clk: mvebu: ap806: introduce a new 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/32e35c1d5919bdf9dc7d58678f0c0b462886d03e.1496239589.git-series.gregory.clement@free-electrons.com