qxl_driver: hide cursors on vt switch
qxl_driver: hide cursors on vt switch

This is not enough to prevent any qxl_destroy_pixmap call during vt
switch, but it prevents those triggered by CursorDisplayCursor.

Note: a matching xf86_show_cursors call doesn't hurt, but is not
required, so not adding it.

It is still possible to access freed memory by the following trigger:

==4416== Invalid read of size 8
==4416==    at 0x5D15EC1: unlink_surface (qxl_surface.c:685)
==4416==    by 0x5D162F9: qxl_surface_kill (qxl_surface.c:799)
==4416==    by 0x5D12688: qxl_destroy_pixmap (qxl_driver.c:928)
==4416==    by 0x55730B: damageDestroyPixmap (damage.c:1556)
==4416==    by 0x51C77B: ShmDestroyPixmap (shm.c:273)
==4416==    by 0x54591B: FreePicture (picture.c:1465)
==4416==    by 0x467A32: doFreeResource (resource.c:873)
==4416==    by 0x467B7E: FreeResource (resource.c:903)
==4416==    by 0x547742: ProcRenderFreePicture (render.c:661)
==4416==    by 0x54B13A: ProcRenderDispatch (render.c:1988)
==4416==    by 0x430670: Dispatch (dispatch.c:428)
==4416==    by 0x492604: main (main.c:288)
==4416==  Address 0x121031e0 is 116,960 bytes inside a block of size 122,880 free'd
==4416==    at 0x4A079AE: free (vg_replace_malloc.c:427)
==4416==    by 0x5D16BDA: qxl_surface_cache_evacuate_all (qxl_surface.c:1060)
==4416==    by 0x5D13078: qxl_leave_vt (qxl_driver.c:1209)
==4416==    by 0x4A4D4F: xf86VTSwitch (xf86Events.c:462)
==4416==    by 0x4A4926: xf86Wakeup (xf86Events.c:285)
==4416==    by 0x43E2E1: WakeupHandler (dixutils.c:421)
==4416==    by 0x488A75: WaitForSomething (WaitFor.c:224)
==4416==    by 0x4303CF: Dispatch (dispatch.c:357)
==4416==    by 0x492604: main (main.c:288)

This is fixed by a following patch to not free all_surfaces, instead
keeping pointers from it to the evacuated list.

dezelin/xf86-video-qxl,facboy/xserver-xorg-video-qxl,dezelin/xf86-video-qxl,facboy/xserver-xorg-video-qxl,dezelin/xf86-video-qxl,fgouget/xf86-video-qxl,fgouget/xf86-video-qxl,fgouget/xf86-video-qxl,facboy/xserver-xorg-video-qxl,facboy/xserver-xorg-video-qxl,fgouget/xf86-video-qxl