Install patchelf on RHEL

Patchelf is needed for fixing FFmpeg dependencies,
the previous CR reveals details.
Patchelf is not available in the standard package manager on RHEL,
let's install it from sources.

Pick-to: 6.8
Change-Id: I724ffed9c48b9811e10de89519d8271e2f82260d
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

coin/provisioning/common/unix/install-ffmpeg.sh

@@ -71,12 +71,7 @@ build_ffmpeg() {
 }
 
 if [ "$os" == "linux" ]; then
-      # TODO: install patchelf on RHEL and remove the force "static"
-  if [ -f "/etc/redhat-release" ]; then
-    build_type="static"
-  else
-    build_type="$2"
-  fi
+  build_type="$2"
 
   install_ff_nvcodec_headers