i965: Add functions for comparing two brw_wm/vs_prog_data structs.

i965: Add functions for comparing two brw_wm/vs_prog_data structs.

Currently, this just avoids comparing all unused parts of param[] and
pull_param[], but it's a step toward getting rid of those giant statically
sized arrays.

v2: Actually use the new function instead of just looking at its
    address.  This required changing the args to const pointers.
    (review by Kenneth)

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