i965: Flip the non-coherent framebuffer fetch extension bit on G45-Gen8 hardware.

i965: Flip the non-coherent framebuffer fetch extension bit on G45-Gen8 hardware.

This is not enabled on the original Gen4 part because it lacks surface
state tile offsets so it may not be possible to sample from arbitrary
non-zero layers of the framebuffer depending on the miptree layout (it
should be possible to work around this by allocating a scratch surface
and doing the same hack currently used for render targets, but meh...).

On Gen9+ even though it should mostly work (feel free to force-enable
it in order to compare the coherent and non-coherent paths in terms of
performance), there are some corner cases like 1D array layered
framebuffers that cannot be handled easily by the non-coherent path
because of the incompatible layout in memory of 1D and 2D miptrees (it
should be possible to work around this too by doing state-dependent
recompiles, but it's hard to care enough since Gen9 has native support
for coherent render target reads...)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>