arm64: defconfig: Enable SND_SOC_WM8978

WM8978 audio CODEC is supported on RZ/G2L SMARC EVK.
Enable it on arm64 defconfig as module.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Link: https://lore.kernel.org/r/20210920093905.10878-1-biju.das.jz@bp.renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>