svga: fix the rasterizer state resets

svga: fix the rasterizer state resets

draw module calls back into the driver and sets certain parts
of the state to whatever it needs, unfortunately unless you
get the ordering of calls to draw just right you'll end up
reseting your own driver state. That's what was happening to us
draw module would under certain conditions reset our own driver
state.

Reviewed-by: Brian Paul <brianp@vmware.com>