arm64: defconfig: Enable OF_OVERLAY option

arm64: defconfig: Enable OF_OVERLAY option

The RP1 driver uses the infrastructure enabled by OF_OVERLAY config
option. Enable that option in defconfig in order to produce a kernel
usable on RaspberryPi5 avoiding to enable it separately.

Signed-off-by: Andrea della Porta <andrea.porta@suse.com>
Reviewed-by: Stefan Wahren <wahrenst@gmx.net>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/r/20250529135052.28398-12-andrea.porta@suse.com
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>