glamor: Require that pixmap depths match for Render copies.

The copy optimization in d37329cba4
replicated a bug from last time we did a copy optimization: CopyArea
is only defined for matching depths.  This is only a problem at 15 vs
16 depth right now (24 vs 32 would also have matching Render formats,
but they should work) but be strict in case we store other depths
differently in the future.

Fixes rendercheck -t blend -o src -f x4r4g4b4,x3r4g4b4

v2: Drop excessive src->depth == dst->depth check that snuck in.
v3: Switch back to src->depth == dst->depth
v4: Touch up commit message (s/bpp/depth).

Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>

glamor/glamor_render.c

@@ -1423,6 +1423,8 @@ glamor_composite_clipped_region(CARD8 op,
     /* Is the composite operation equivalent to a copy? */
     if (!mask && !source->alphaMap && !dest->alphaMap
         && source->pDrawable && !source->transform
+        /* CopyArea is only defined with matching depths. */
+        && dest->pDrawable->depth == source->pDrawable->depth
         && ((op == PictOpSrc
              && (source->format == dest->format
                  || (PICT_FORMAT_COLOR(dest->format)