AMDGPU: Stop validating earlyclobber operands in assembler

This validation was introduced in D34003 for v_qsad/v_mqsad instructions
but it applies to all instructions with earlyclobber operands, which now
includes v_mad_i64/v_mad_u64.

In all these cases I do not think there is documentation saying that the
destination must not overlap the sources. Rather there are *some* cases
where the instruction may not function correctly if there is an overlap,
and we are using earlyclobber as a conservative way of preventing
codegen from generating those cases.

I think it is unhelpful for the assembler to enforce the earlyclobber
restriction because it prevents assembling cases where the programmer
knows that in fact the overlap is safe.

See also: https://github.com/llvm/llvm-project/issues/57610

Differential Revision: https://reviews.llvm.org/D134272