[Intel-gfx] xfce panel problem with SNA, not with UXA

[Grant]

My xfce hidden panel looks great docked to the top, bottom, or right side
of the screen, but if it's docked to the left side it looks weird when
unhidden if I'm using SNA.  The problem does not appear if I use UXA.
By weird I mean the background gray color has a darker gray pattern
running through it.  I can attach a screenshot if necessary.  Others
have reported this on the xfce list.  Please let me know if I should
file a bug.

- Grant