nir: detect more induction variables

nir: detect more induction variables

This allows loop analysis to detect inductions variables that
are incremented in both branches of an if rather than in a main
loop block. For example:

   loop {
      block block_1:
      /* preds: block_0 block_7 */
      vec1 32 ssa_8 = phi block_0: ssa_4, block_7: ssa_20
      vec1 32 ssa_9 = phi block_0: ssa_0, block_7: ssa_4
      vec1 32 ssa_10 = phi block_0: ssa_1, block_7: ssa_4
      vec1 32 ssa_11 = phi block_0: ssa_2, block_7: ssa_21
      vec1 32 ssa_12 = phi block_0: ssa_3, block_7: ssa_22
      vec4 32 ssa_13 = vec4 ssa_12, ssa_11, ssa_10, ssa_9
      vec1 32 ssa_14 = ige ssa_8, ssa_5
      /* succs: block_2 block_3 */
      if ssa_14 {
         block block_2:
         /* preds: block_1 */
         break
         /* succs: block_8 */
      } else {
         block block_3:
         /* preds: block_1 */
         /* succs: block_4 */
      }
      block block_4:
      /* preds: block_3 */
      vec1 32 ssa_15 = ilt ssa_6, ssa_8
      /* succs: block_5 block_6 */
      if ssa_15 {
         block block_5:
         /* preds: block_4 */
         vec1 32 ssa_16 = iadd ssa_8, ssa_7
         vec1 32 ssa_17 = load_const (0x3f800000 /* 1.000000*/)
         /* succs: block_7 */
      } else {
         block block_6:
         /* preds: block_4 */
         vec1 32 ssa_18 = iadd ssa_8, ssa_7
         vec1 32 ssa_19 = load_const (0x3f800000 /* 1.000000*/)
         /* succs: block_7 */
      }
      block block_7:
      /* preds: block_5 block_6 */
      vec1 32 ssa_20 = phi block_5: ssa_16, block_6: ssa_18
      vec1 32 ssa_21 = phi block_5: ssa_17, block_6: ssa_4
      vec1 32 ssa_22 = phi block_5: ssa_4, block_6: ssa_19
      /* succs: block_1 */
   }

Unfortunatly GCM could move the addition out of the if for us
(making this patch unrequired) but we still cannot enable the GCM
pass without regressions.

This unrolls a loop in Rise of The Tomb Raider.

vkpipeline-db results (VEGA):

Totals from affected shaders:
SGPRS: 88 -> 96 (9.09 %)
VGPRS: 56 -> 52 (-7.14 %)
Spilled SGPRs: 0 -> 0 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 2168 -> 4560 (110.33 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 4 -> 4 (0.00 %)
Wait states: 0 -> 0 (0.00 %)

Reviewed-by: Thomas Helland <thomashelland90@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=32211