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>