ARM: mach-shmobile: mackerel: add ak4642 amixer settings on comment

current ak4642 needs amixer settings for playing which was not
needed on old kernel.
This patch show it on comment area

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>