package/weston: requires host-pkgconf

weston's configure.ac uses PKG_CHECK_MODULES,
so it needs to depend on host-pkgconf.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>