nv50/ir: handle SHLADD in IndirectPropagation

nv50/ir: handle SHLADD in IndirectPropagation

An alternative solution to the problem fixed in
0bd83d0 ("nv50/ir: move LateAlgebraicOpt to the very end").

total instructions in shared programs : 5481195 -> 5480808 (-0.01%)
total gprs used in shared programs    : 647535 -> 647530 (-0.00%)
total shared used in shared programs  : 389120 -> 389120 (0.00%)
total local used in shared programs   : 21064 -> 21064 (0.00%)
total bytes used in shared programs   : 58555784 -> 58551648 (-0.01%)

                local     shared        gpr       inst      bytes
    helped           0           0           2          34          34
      hurt           0           0           0           0           0