When GDK_SCALE is != 1 and egl is used, the image presented does not
fit to the window (scale of 2 is often used with hidpi monitors).
Usually this is not a problem since all components are adjusted by
gdk/gtk but with egl, pixel-based data is not being scaled. In this
case window's scale value can be used in order to determine whether
to use a pixel resource with higher resolution data.

In order to reproduce the problem set spice with virgl/Intel-vGPU
and run spice-gtk with GDK_SCALE=2

This issue was also reported at freedesktop gitlab repo:
#99



Signed-off-by: Snir Sheriber <ssheribe@redhat.com>
Acked-by: Victor Toso <victortoso@redhat.com>