Add support for nv21 video format as found on android

Note that the same code could be used for nv12
10 jobs for qrcode-nv21-by-sschmeisser in 19 minutes and 52 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Test
passed #16629
clazy

00:03:17

passed #16630
qmllint

00:02:36

 
  Build
passed #16634
archlinux

00:03:31

passed #16633
debian-sid

00:03:27

passed #16632
neon-bionic

00:01:22

passed #16631
ubuntu-trusty

00:01:26

 
  Deploy
failed #16637
allowed to fail
android

00:00:01

failed #16635
allowed to fail
linux-appimage

00:02:25

passed #16638
allowed to fail
mac-osxcross

00:09:01

passed #16636
allowed to fail
windows-mxe

00:09:14

 
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/jbbgameich/kaidan/build/CMakeFiles/CMakeOutput.log".
ERROR: Job failed: exit code 1