qtimageformats: allow empty qtimageformats package

This fixes installing qtimageformats-dev with opkg as it depends on the
qtimageformats package which wasn't created.

The qtimageformats package was not created as it is empty and BitBake
avoids producing empty packages by default. The installed files consist
of source files split into qtimageformats-dbg, CMake files split into
qtimageformats-dev, plugins split into qtimageformats-plugins and
debug build of plugins split into qtimageformats-plugins-dbg.

Signed-off-by: Jonathan Liu <net147@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
packagegroup-qt5-toolchain-target: include all modules for development

This adds the necessary target packages for development with all of the
Qt 5 modules.

Signed-off-by: Jonathan Liu <net147@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>