meson: detect opengl api from -base .pc files correctly
requested to merge tpm/gst-plugins-good:meson-opengl-fix-enabled-gl-apis-in-pkgconfig-file into 1.14
There was a mismatch between the .pc files generated by autotools and by meson that would lead to meson not detecting that opengl api is available even though it is, if -base was built with autotools. The mismatch has now been rectified in -base, but we still check the old one for backwards compatibility.
This is mostly for consistency, this problem didn't seem to affect anything in -good.