i965: Use the surface format table to determine render target supportedness.

i965: Use the surface format table to determine render target supportedness.

This moves any chipset-dependent logic we want for render target
format choices to init time as well.  There is still logic left at
state update for SRGB handling, where format choices change based on
GL state.

The brw_render_target_supported() function should now return correct
results, instead of relying on the limited results from
intel_span_supports_format() to avoid lying about FBO completeness.

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