i965: Index sampler program key data by linker-assigned index.

i965: Index sampler program key data by linker-assigned index.

Now that most things are based on the linker-assigned index, it makes
sense to convert the arrays in the VS/WM program key as well.  It seems
silly to leave them indexed by texture unit.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>