configure: require pkg-config for libvmaf

This patch makes the libvmaf filter use pkg-config to detect
and link to libvmaf.
Signed-off-by: Ashish Singh <ashk43712@gmail.com>
Signed-off-by: Ronald S. Bultje <rsbultje@gmail.com>

configure

@@ -5920,8 +5920,7 @@ enabled libtwolame        && require libtwolame twolame.h twolame_init -ltwolame
                                die "ERROR: libtwolame must be installed and version must be >= 0.3.10"; }
 enabled libv4l2           && require_pkg_config libv4l2 libv4l2.h v4l2_ioctl
 enabled libvidstab        && require_pkg_config "vidstab >= 0.98" vid.stab/libvidstab.h vsMotionDetectInit
-enabled libvmaf           && { check_lib libvmaf "libvmaf.h" "compute_vmaf" -lvmaf -lstdc++ -lpthread -lm ||
-                               die "ERROR: libvmaf must be installed"; }
+enabled libvmaf           && require_pkg_config libvmaf libvmaf.h compute_vmaf
 enabled libvo_amrwbenc    && require libvo_amrwbenc vo-amrwbenc/enc_if.h E_IF_init -lvo-amrwbenc
 enabled libvorbis         && require_pkg_config vorbis vorbis/codec.h vorbis_info_init &&
                              require_pkg_config vorbisenc vorbis/vorbisenc.h vorbis_encode_init