build: add option --enable-goa
build: add option --enable-goa

When this option is on, macro GOA_ENABLED is defined to 1 if GOA is
present in the system. Otherwise error message is raised.

Default: auto

https://bugzilla.gnome.org/show_bug.cgi?id=697565

MikePetullo/grilo-plugins,jasuarez/grilo-plugins,MathieuDuponchelle/grilo-plugins,MathieuDuponchelle/grilo-plugins,vrutkovs/grilo-plugins,GNOME/grilo-plugins,GNOME/grilo-plugins,kyoushuu/grilo-plugins,MathieuDuponchelle/grilo-plugins,vrutkovs/grilo-plugins,MikePetullo/grilo-plugins,MathieuDuponchelle/grilo-plugins,grilofw/grilo-plugins,kyoushuu/grilo-plugins,kyoushuu/grilo-plugins,vrutkovs/grilo-plugins,vrutkovs/grilo-plugins,jasuarez/grilo-plugins,grilofw/grilo-plugins,MikePetullo/grilo-plugins