package_rpm.bbclass: support packaging of symlinks to directories

package_rpm.bbclass: support packaging of symlinks to directories

os.walk() returns symlinks to directories in the "dirs" lists,
but then never enters them by default. As a result, the old
code applied neither the directory handling (because that
is active once a directory gets entered) nor the file handling
and thus never packaged such symlinks.

The fix is simple: find such special directory entries and move
them to the "files" list.

Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>