Add support for Symbian ICL to QVGPixmapData

On devices such as the N8, Qt is configured to use the OpenVG graphics system. The backend for QPixmap on this graphics system is QVGPixmapData and this class stores data in a QImage and when the data is required on the screen, a VGImage is allocated from Qt's VG image pool and the data is uploaded to this image and drawn on screen.

In the event that the Symbian ICL adds support for hardware based bitmaps such as EGLImage, Qt should try to use this API to decode the image more efficiently.

There are 2 functions in the base class (QPixmapData) that should be optimized to use the Symbian ICL wherever possible:

virtual bool fromFile(const QString &filename, const char *format,
                          Qt::ImageConversionFlags flags);
    virtual bool fromData(const uchar *buffer, uint len, const char *format,
                          Qt::ImageConversionFlags flags);

Implementing these functions using the ICL should provide a more optimized way to get decoded data into a VGImage