plymouth: disable building documentation explicitly
plymouth: disable building documentation explicitly

Signed-off-by: Toshiko YOSHIDA <311de952d79aff7d5c68e1437a41a732e1c05c82@toshiba.co.jp>

tienlee/meta-debian,tienlee/meta-debian,tienlee/meta-debian,meta-debian/meta-debian,tienlee/meta-debian,meta-debian/meta-debian,tienlee/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian,tienlee/meta-debian,meta-debian/meta-debian