glamor: Pass depth to glamor_pm_is_solid and glamor_set_planemask

Instead of passing the destination drawable, just pass the depth, as
the underlying functions need only that to check whether the planemask
is going to work.

This API change will allow higher level functions to not need the
destination pixmap.

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

glamor/glamor_text.c

@@ -431,7 +431,7 @@ glamor_image_text(DrawablePtr drawable, GCPtr gc,
         /* Check planemask before drawing background to
          * bail early if it's not OK
          */
-        if (!glamor_set_planemask(pixmap, gc->planemask))
+        if (!glamor_set_planemask(gc->depth, gc->planemask))
             goto bail;
         for (c = 0; c < count; c++)
             if (charinfo[c])