libs: encoder: mpeg2: Add highP level for 1080@50p/60p.

The MPEG2 spec has amendment 3 to introduce a new level highP, which
is used for 1080@50p/60p streams. We need to add this level to avoid
encoding failure because of the level check.

Fix: #306
Part-of: <!432>
18 jobs for master in 15 minutes and 2 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build Docker
passed alpine amd64 manifest builder docker #11196750

00:00:30

passed android docker #11196749

00:00:35

passed cerbero fedora amd64 docker #11196748

00:00:36

passed fedora amd64 docker #11196747

00:14:48

passed gst-indent amd64 docker #11196751

00:00:30

passed windows amd64 docker #11196752
windows shell 1809

00:00:11

 
  Preparation
passed gst indent #11196754

00:00:14

manual manifest #11196753
manual
 
  Build
created build clang fedora x86_64 #11196758
created build nodebug fedora x86_64 #11196755
created build static fedora x86_64 #11196756
created build static nodebug fedora x86_64 #11196757
 
  Test
created check fedora #11196759
gstreamer
created integration testsuites fedora 1/4 #11196760
gstreamer
created integration testsuites fedora 2/4 #11196761
gstreamer
created integration testsuites fedora 3/4 #11196762
gstreamer
created integration testsuites fedora 4/4 #11196763
gstreamer
 
  Integrate
created documentation #11196764