[AArch64] Improve loop unrolling performance on Cavium T99
This patch improves performance on Cavium T99 as shown here (libquantum 0.2.4):
By increasing the LoopMicroOpsBufferSize in the Cavium T99 Scheduler file,
loop unrolling becomes more aggressive. This helps performance on T99.
Test case included.
Patch by Stefan Teleman
Differential Revision: https://reviews.llvm.org/D40695