configs/rock5b: enable mdev to enable automatic module loading

Enable mdev so that coldplug will automatically load kernel modules that
were unavailable before rootfs was mounted.

mdev will also enable hotplug so that kernel modules will be automatically
loaded when a new device is inserted in e.g. USB or PCIe after boot.

Before this change:
$ lsmod | wc -l
0

After this change:
$ lsmod | wc -l
43

Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

configs/rock5b_defconfig

@@ -47,6 +47,7 @@ BR2_PACKAGE_HOST_DTC=y
 BR2_PACKAGE_HOST_GENIMAGE=y
 BR2_PACKAGE_HOST_MTOOLS=y
 BR2_SYSTEM_DHCP="eth0"
+BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV=y
 BR2_ROOTFS_POST_BUILD_SCRIPT="board/radxa/rock5b/post-build.sh"
 BR2_ROOTFS_POST_IMAGE_SCRIPT="support/scripts/genimage.sh"
 BR2_ROOTFS_POST_SCRIPT_ARGS="-c board/radxa/rock5b/genimage.cfg"