i965: Add 2x MSAA support to the MCS allocation function.

2x MSAA also uses 8 bits, just like 4x.  More bits are unused.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

src/mesa/drivers/dri/i965/intel_mipmap_tree.c

@@ -1251,6 +1251,7 @@ intel_miptree_alloc_mcs(struct brw_context *brw,
     */
    mesa_format format;
    switch (num_samples) {
+   case 2:
    case 4:
       /* 8 bits/pixel are required for MCS data when using 4x MSAA (2 bits for
        * each sample).