glsl: Store ir_variable_data::_num_state_slots and ::binding in 16-bits each

glsl: Store ir_variable_data::_num_state_slots and ::binding in 16-bits each

Valgrind massif results for a trimmed apitrace of dota2:

                  n        time(i)         total(B)   useful-heap(B) extra-heap(B)    stacks(B)
Before (32-bit): 44 40,577,049,140       68,118,608       62,441,063     5,677,545            0
After  (32-bit): 71 40,583,408,411       67,761,528       62,263,519     5,498,009            0

Before (64-bit): 63 37,122,829,194       95,153,008       87,333,600     7,819,408            0
After  (64-bit): 67 37,123,303,706       95,150,544       87,333,600     7,816,944            0

A real savings of 173KiB on 32-bit and no change on 64-bit.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>