documentation.

This phy is only used on STiH415/6 based silicon, and support for
these SoC's is being removed from the kernel.
Signed-off-by: NPeter Griffin <peter.griffin@linaro.org>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NKishon Vijay Abraham I <kishon@ti.com>