[LV][AArch64] Resolve test failure due use of unordered container

AArch64/reg-usage.ll has an issue with the output ordering due to use of unordered container. This was discovered by -DLLVM_REVERSE_ITERATION:BOOL=ON
cmake option.
This patch tries to address it by making use of ordered container.

Differential Revision: https://reviews.llvm.org/D145472/