i965/blorp: Update the fast clear value buffer.

i965/blorp: Update the fast clear value buffer.

On Gen10, whenever we do a fast clear, blorp will update the clear color
state buffer for us, as long as we set the clear color address
correctly.

However, on a hiz clear, if the surface is already on the fast clear
state we skip the actual fast clear operation and, before gen10, only
updated the miptree. On gen10+ we need to update the clear value state
buffer too, since blorp will not be doing a fast clear and updating it
for us.

v4:
 - do not use clear_value_size in the for loop
 - Get the address of the clear color from the aux buffer or the
 clear_color_bo, depending on which one is available.
 - let core blorp update the clear color, but also update it when we
 skip a fast clear depth.

v5: Better subject (Jordan).
v6: Remove outdated comment (Jason).

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