The Android plugin had a function to convert from NV21 to RGB32.
It's now moved to the Qt Multimedia library and it supports additional
source formats. It could be further improved with more SIMD code, it
could then become a public API.

Change-Id: Ibee349027048a263a1a7ea74dc51237f7747912c
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>