Add pins, groups, and a function for SCIF_CLK, which is the external
clock source for the Baud Rate Generator for External Clock (BRG) on
(H)SCIF.
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Acked-by: NLinus Walleij <linus.walleij@linaro.org>