arm64: defconfig: Enable DRM DU and V4L2 FCP + VSP modules

Extend the ARM64 defconfig to enable the DU DRM device as module
together with required dependencies of V4L2 FCP and VSP modules.

This enables VGA output on the r8a7795 Salvator-X board.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>