intel/genxml: Normalize URB Data field in WM_STATE.

intel/genxml: Normalize URB Data field in WM_STATE.

On gen6+, this is called "Dispatch GRF Start Register For Constant/Setup Data
0", while on gen5 and lower it's called only "Dispatch GRF Start Register For
URB Data", but it's essentially the same thing (URB data), so rename it to
match newer gens and simplify the C code that handles it.

Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>