update kernel to the latest sunxi-3.0

Signed-off-by: Alejandro Mery <amery@geeks.cl>
mk_hwpack: make uboot.cmd also optional on android

Signed-off-by: Alejandro Mery <amery@geeks.cl>
mk_hwpack.sh: add uEnv.txt (optional) support

Signed-off-by: Alejandro Mery <amery@geeks.cl>