image_types_wic.bbclass: tighten dependency to help do_rm_work_all

image_types_wic.bbclass: tighten dependency to help do_rm_work_all

Depending on wic-tools:do_build pulls a lot of additional, indirect
dependencies into the image sysroot during do_image_wic as soon as
rm_work.bbclass is active, because then we have
do_build->do_rm_work_all->[all dependencies]. One of those
dependencies is libgcc-initial, which clashes with libgcc itself,
leading to errors in extend_recipe_sysroot like this:

   Exception: FileExistsError: [Errno 17] File exists: '.../tmp/sysroots-components/corei7-64/glibc-initial/usr/include/fstab.h' -> '.../tmp/work/intel_corei7_64-poky-linux/core-image-minimal/1.0-r0/recipe-sysroot/usr/include/fstab.h'

As the image recipe only needs the sysroot of wic-tools and does not
need to wait for the build of wic-tools to finish, depending on
do_populate_sysroot is the better choice and happens to avoid
the problem above.

Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>