anv: Initialize the clear color more often for FCV

anv: Initialize the clear color more often for FCV

Instead of only initializing the clear color when the first subresource
is accessed, initialize it for every FCV-enabled subresource. This is
needed because writes to any subresource may be converted to fast
clears.

Now that init_fast_clear_color is called for every subresource, we take
care not to stomp on the fast-clear-tracking state of the first
subresource by moving the code which updates it outside of
init_fast_clear_color.

Now init_fast_clear_color does just what it says: initializes the fast
clear color.

This fixes the regression introduced with commit 57445adc891,
("anv: Re-enable CCS_E on TGL+").

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/8461
Reviewed-by: Rohan Garg <rohan.garg@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24857>