Add support for nv21 video format as found on android

Note that the same code could be used for nv12
10 jobs for master in 12 minutes and 50 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #16641
clazy

00:01:25

passed #16642
qmllint

00:01:24

 
  Build
passed #16646
archlinux

00:01:51

passed #16645
debian-sid

00:01:41

passed #16644
neon-bionic

00:01:27

passed #16643
ubuntu-trusty

00:01:27

 
  Deploy
failed #16649
allowed to fail
android

00:00:01

failed #16647
allowed to fail
linux-appimage

00:00:54

passed #16650
allowed to fail
mac-osxcross

00:05:25

passed #16648
allowed to fail
windows-mxe

00:05:09

 
Name Stage Failure
failed
android Deploy
Running with gitlab-runner 11.11.2 (ac2a293c)
on fiesta umZyLAru
Using Docker executor with image kdeorg/android-sdk ...
Pulling docker image kdeorg/android-sdk ...
ERROR: Job failed: Error response from daemon: pull access denied for kdeorg/android-sdk, repository does not exist or may require 'docker login' (executor_docker.go:175:1s)
failed
linux-appimage Deploy
 * KF5Notifications
* Qt5Widgets, Integration with QWidget based desktop styles
* Qt5Qml
* Qt5Core
* Qt5

-- Configuring incomplete, errors occurred!
See also "/builds/kde/kaidan/build/CMakeFiles/CMakeOutput.log".
ERROR: Job failed: exit code 1