AMDGPU/MC: Fix emitting absolute expressions (#136789)
When absolute MCExprs appear in normal instruction operands, we have to
emit them like a normal inline constant or literal. More generally, an
MCExpr that happens to have an absolute evaluation should be treated
exactly like an immediate operand here.
No test; I found this downstream, and I don't think it can be triggered
upstream yet.
Fixes: 16238669 ("[AMDGPU][MC] Support UC_VERSION_* constants. (#95618)")
