libsoup: bump to version 2.52.1

Disabled vala bindings since they're not used by the current buildroot
packages and it requires gobject-introspection which we don't provide
yet.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>