[DAGCombine] Do not fold SRA/SRL of MUL into MULH when MUL's LSB are

used, and MUL_LOHI is available

Folding into a sra(mul) / srl(mul) into a mulh introduces an extra
multiplication to compute the high half of the multiplication,
while it is more profitable to compute the high and lower halfs with a
single mul_lohi.

Differential Revision: https://reviews.llvm.org/D133768