[Xorg] Making small changes to the XAA layer

[Alan Cox]

I've been chasing a couple of bug reports in my Voodoo2 driver as well
as looking at performance problems previously. I've hit two things 
where XAA doesn't "do the right thing" for the hardware

1.	ColorExpandFill has no NO_GXCOPY support that I can find, unlike the
other relevant operations. This would speed Voodoo2 up a little but is a
minor item

2.	When uploading image data the Voodoo2 needs to wait for the
accelerator to idle each scan line end, which also has no XAA option.

The changes seem pretty small but I'd like to be sure that whacking the
XAA layer is the right place to fix these limitations.

Alan