Makefile:Make $(SD_CARD) detection simpler

Signed-off-by: Jari Helaakoski <tekkuli@gmail.com>
mk_livesuit_img.sh:Force symbolic link operation.

Signed-off-by: Jari Helaakoski <tekkuli@gmail.com>
mk_ext4_rootfs.sh/:Fail if unpacking fails

Signed-off-by: Jari Helaakoski <tekkuli@gmail.com>
Makefile:livesuit target supports now multiple rootfs instances

Signed-off-by: Jari Helaakoski <tekkuli@gmail.com>
update allwinner-tools submodule

Signed-off-by: Jari Helaakoski <tekkuli@gmail.com>