Improve drawing scaled image with raster using SSE2

Improve drawing scaled image with raster using SSE2

That codepath is taken in qml when an Image specify with and hight and
is not smooth, and the image contains alpha contents

The changes in qdrawingprimitive_sse2_p.h just put some code from the
BLEND_SOURCE_OVER_ARGB32_SSE2 macro into a sub macro to allow its reuse

The code that is not SSE2 in qt_scale_image_argb32_on_argb32_sse2 comes
from the qt_scale_image_argb32_on_argb32 in qblendfunctions.cpp

Change-Id: I071a040af4514fb21777dead9f7c5baf16071d59
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>