apache2: add PACKAGECONFIG for selinux

Add PACKAGECONFIG for 'selinux', otherwise there would be warnings like
below:

WARN: apache2: apache2 rdepends on libselinux, but it isn't a build dependency?

Signed-off-by: Wenzong Fan <wenzong.fan@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>