mesa/st: Generates TGSI that always recognizes INSTANCEID/VERTEXID as integers.

mesa/st: Generates TGSI that always recognizes INSTANCEID/VERTEXID as integers.

Tested by running piglit draw-instanced, and by forcing llvmpipe advertise no native
integer support, which now produces:

VERT
DCL IN[0]
DCL SV[0], INSTANCEID
DCL OUT[0], POSITION
DCL OUT[1], COLOR
DCL CONST[0..19]
DCL TEMP[0], LOCAL
DCL TEMP[1], LOCAL
DCL TEMP[2], LOCAL
DCL ADDR[0]
  0: U2F TEMP[0].x, SV[0]
  1: ARL ADDR[0].x, TEMP[0].xxxx
  2: MOV TEMP[1].xy, CONST[ADDR[0].x+8].xyxx
  3: ADD TEMP[2].x, IN[0].xxxx, TEMP[1].xxxx
  4: ADD TEMP[1].x, IN[0].yyyy, TEMP[1].yyyy
  5: MUL TEMP[2], CONST[16], TEMP[2].xxxx
  6: MAD TEMP[2], CONST[17], TEMP[1].xxxx, TEMP[2]
  7: MAD TEMP[2], CONST[18], IN[0].zzzz, TEMP[2]
  8: MAD TEMP[2], CONST[19], IN[0].wwww, TEMP[2]
  9: ARL ADDR[0].x, TEMP[0].xxxx
 10: MOV TEMP[1], CONST[ADDR[0].x]
 11: MOV OUT[0], TEMP[2]
 12: MOV OUT[1], TEMP[1]
 13: END