image_types.bbclass: Rebuild when WICVARS change

image_types.bbclass: Rebuild when WICVARS change

The procces to do a wic image is to save a file with
variables required by wic and then call wic using this
file. Because this is external to bitbake if the vars
change, the image won't be rebuild; an example of such
is IMAGE_BOOT_FILES.

This patch adds these variables to vardeps of do_rootfs
when a wic image is build. This will rebuild the image
if a variable needed by wic changes.

[YOCTO #8693]

(From OE-Core rev: 12c54d50ed4c321dc272beb3c6cb770965c979f1)

Signed-off-by: Mariano Lopez <mariano.lopez@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>