ARM: shmobile: defconfig: Enable RZ/A1H RTC support

Enable support for the RZ/A1H Realtime Clock, which is used on the
Genmai and RSK+RZA1 boards.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200624131931.3686-8-geert+renesas@glider.be