i965/fs: Track the binding table size in brw_wm_prog_data.

i965/fs: Track the binding table size in brw_wm_prog_data.

By tracking the maximum surface index used by the shader, we know just
how small we can make the binding table.

Since it depends entirely on the shader program, we can just compute
it once at compile time, rather than at binding table emit time (which
happens during drawing).

v2: Store binding_table_size, rather than max_surface_index, for
    consistency with the VS (which needs to be able to represent 0
    surfaces).

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