[AMDGPU] Legalize operands of V_ADDC_U32_e32 and friends

These instructions have an implicit use of vcc which counts towards the
constant bus limit. Pre gfx10 this means that the explicit operands
cannot be sgprs. Use the custom inserter hook to call legalizeOperands
to enforce that restriction.

Fixes https://bugs.llvm.org/show_bug.cgi?id=51217

Differential Revision: https://reviews.llvm.org/D106868