Inplace versions of QImage rgbSwapped() and mirrored() for rvalue refs

Adds inplace version of QImage::rgbSwapped() and QImage::mirrored() that
can be used on temporary QImage objects when supported by the compiler.

[ChangeLog][QtGui][QImage]Rvalue qualified mirrored and rgbSwapped methods for inline conversions
Change-Id: I4ffb658bf620dfc472d9db14c1aa70291c1fd842
Reviewed-by: Gunnar Sletta <gunnar.sletta@jollamobile.com>