[LegalizeTypes] Don't assume fshl/fshr shift amount type matches the other operands.

Like other shifts, the type isn't required to match. We shouldn't
assume we can call ZExtPromotedInteger.

I tested the PromoteIntOp_FunnelShift locally by removing the promotion
of the shift amount from PromoteIntRes_FunnelShift. But with the final
version of this patch it is never executed on any tests.

Differential Revision: https://reviews.llvm.org/D125106