anv: Make blorp update the clear color.

anv: Make blorp update the clear color.

Instead of updating the clear color in anv before a resolve, just let
blorp handle that for us during fast clears.

v5: Update comment about HiZ clear color (Jordan).

Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>