udev: ensure /dev mgmt option is in sync

These options should be in sync, both for consistency and because udev
needs devtmpfs enabled in the kernel.

We unfortunately cannot just select BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_UDEV
here, as that one selects udev - leading to recursion erors, so instead
we use depends on.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>