uxa: Initialise lists for private pixmap structure.

When updating a buffer object for the framebuffer, we may need to
allocate a fresh pixmap private structure, for example if the pixmap is
replaced due to resize. When doing so it is then imperative to
initialise the circularly linked lists correctly.

Should fix the fault:
  #0  i830_set_pixmap_bo (pixmap=0x24ab380, bo=0x24ab780) at i830_uxa.c:524
  #1  0x00007f8615c629fd in drmmode_xf86crtc_resize (scrn=0x247a320, width=1280, height=800) at drmmode_display.c:1345
  #2  0x000000000051246c in xf86RandR12ScreenSetSize (pScreen=0x24824f0, width=<value optimized out>, height=<value optimized
 out>, mmWidth=<value optimized out>, mmHeight=<value optimized out>) at xf86RandR12.c:709
  #3  0x0000000000512aa8 in xf86RandR12CreateScreenResources (pScreen=<value optimized out>) at xf86RandR12.c:839
  #4  0x0000000000514ec0 in xf86CrtcCreateScreenResources (screen=0x24824f0) at xf86Crtc.c:727
  #5  0x0000000000424fb3 in main (argc=<value optimized out>, argv=<value optimized out>, envp=<value optimized out>) at main.c:215
as reported by 'buscher'.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

src/i830_uxa.c

@@ -530,6 +530,9 @@ void i830_set_pixmap_bo(PixmapPtr pixmap, dri_bo * bo)
 			priv = xcalloc(1, sizeof (struct intel_pixmap));
 			if (priv == NULL)
 				goto BAIL;
+
+			list_init(&priv->batch);
+			list_init(&priv->flush);
 		}
 
 		dri_bo_reference(bo);