build,meson: If QMI disabled, don't build qcom-soc plugin
The non-QMI build in meson is currently failing because we're trying to build the qcom-soc plugin, and we shouldn't do that if QMI is not supported.
Easy to reproduce:
$ meson setup build --prefix=/usr --sysconfdir=/etc --localstatedir=/var -Dgtk_doc=true -Dqmi=disabled -Dqrtr=disabled
$ ninja -C build
@inigomartinez FYI