make_rootfs.sh: Support building ubuntu with KDE
make_rootfs.sh: Support building ubuntu with KDE

Support option kde for building Ubuntu 18.04.2 image for
A64-Teres with kde-plasma-desktop. This image uses the same
repositories as bionic.

Signed-off-by: Leon Anavi <be92910ae7bb6f58bb9b7c6f845bc30640119592@anavi.org>

OLIMEX/DIY-LAPTOP,OLIMEX/DIY-LAPTOP,OLIMEX/DIY-LAPTOP,OLIMEX/DIY-LAPTOP,OLIMEX/DIY-LAPTOP,OLIMEX/DIY-LAPTOP