rp-pppoe: Fix rootfs creation errors

error: file /usr/share/doc/README from install of rp-pppoe-doc-3.11-*
conflicts with file from package dmidecode-doc-2.12*

Signed-off-by: Li Xin <lixin.fnst@cn.fujitsu.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Armin Kuster <akuster808@gmail.com>