We are flushing tile cache more often than is necessary. In
unified cache mode, tile cache flushing is expensive, evicting all
depth/pixel data from the L3$. This is only need for a handful of
cases, such as: making cpu or gpu changes globally visible
(e.g. map), fast color clears, or slow depth clears. Tile cache
flushing is a gen12+ feature.

Remove blanket flushing of tile cache on all depth/RT flushes.
Replace with selective tile cache flushing.

Improves performance in several workloads:
AztecRuins.ogl-high-offscreen-1440p 1%
UnigineValley.ogl-g2                1%
Dota 2 (replay Jul 2020).ogl-g2     1%
Counter-Strike GO.ogl-g2            1%
Manhattan.ogl-Off-19x10             2%
CarChase.ogl-Off-19x10              1%
Bioshock Infinite.ogl-g2            1%

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <!10217>