pinctrl: sh-pfc: r8a7794: Add audio clock pin groups

Add the audio clock pin groups to the R8A7794 PFC driver.

[Sergei:  fixed pin group names to reflect the reality, fixed pin names in
the comments to *_pins[], lowercased the separator comment, resolved rejects,
added the changelog, renamed the patch.]

Signed-off-by: Ryo Kataoka <ryo.kataoka.wt@renesas.com>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>