The ARGB32PM code-path doesn't have enough precision to accurately
render ARGB32 images, but the RGB64 code-path does. Since this is
already a slow configuration and the most costly part is the conversion
we can switch to the more accurate code-path for little cost.
Task-number: QTBUG-55720
Change-Id: Ifa0afba8d8cc0c2f699bb91f51726f4ee5228f3e
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>