anv/blorp/clear_subpass: Only set surface clear color for fast clears

anv/blorp/clear_subpass: Only set surface clear color for fast clears

Not all clear colors are valid.  In particular, on Broadwell and
earlier, only 0/1 colors are allowed in surface state.  No CTS tests are
affected outright by this because, apparently, the CTS coverage for
different clear colors is pretty terrible.  However, when multisample
compression is enabled, we do hit it with CTS tests and this commit
prevents regressions when enabling MCS on Broadwell and earlier.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Cc: "13.0 17.0" <mesa-stable@lists.freedesktop.org>