ARM: shmobile: defconfig: Enable DA9063 ONKEY support

Enable support for the "ONKEY" of the Dialog DA9063 PMIC, which is used
on the Stout and Silk boards.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200624131931.3686-3-geert+renesas@glider.be