oniro-image-base-dev: add ROOTFS_PARTITION_SIZE

Add ROOTFS_PARTITION_SIZE and set it to 2G to fix an error in
do_image_wic where the rootfs "/" size is greater than it's limit.

Signed-off-by: Davide Gardenal <davide.gardenal@huawei.com>

meta-oniro-core/recipes-core/images/oniro-image-base-dev.bb

@@ -12,3 +12,5 @@ IMAGE_INSTALL:append = "\
     "
 
 EXTRA_IMAGE_FEATURES += "dev-pkgs dbg-pkgs src-pkgs tools-sdk tools-debug tools-profile"
+
+ROOT_PARTITION_SIZE = "2G"