RValue ref version of QPixmap::fromImage()

When converting from a temporary image we can use inplace conversion
since we don't have to worry about changes made to the original.

This should give a speedup in several places where QPixmaps are made
from
the return values of methods returning QImages.

Change-Id: I1835bcf3fc061c4dbbb3d0507ec84178dc49b29b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>