arm64: defconfig: enable R8A774C0 SoC

Enable the Renesas RZ/G2E (R8A774C0) SoC in the ARM64 defconfig.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>