image: Add missing depends on virtual/kernel for depmod data

image: Add missing depends on virtual/kernel for depmod data

We need the depmod data so that the kernel depmod command works successfully
at rootfs time. The fact this was working inconsistently is now highlighted
after the command was made to error out. A simple test case is:

bitbake virtual/kernel image
bitbake vrituak/kernel -c clean
bitbake image -c rootfs -f

We fix it by adding the missing dependency, the data is in PKGDATA_DIR and
hence we use packagedata.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>