iris: Invalidate caches only before first Level.
What does this MR do and why?
iris: Invalidate caches only before first Level.
Since each read of generateMipmap is for a different LOD texture, which is unaffected by previous cache states.
Therefore it can invalidate caches only before rendering first level and skip remaining levels
to improve the efficiency of generateMipmap.
Signed-off-by: Huang Rui <rui1.huang@intel.com>
Edited by vickyruirui