[AArch64] Vulcan is now ThunderXT99

Broadcom Vulcan is now Cavium ThunderX2T99.

LLVM Bugzilla: http://bugs.llvm.org/show_bug.cgi?id=32113

Minor fixes for the alignments of loops and functions for
ThunderX T81/T83/T88 (better performance).

Patch was tested with SpecCPU2006.

Patch by Stefan Teleman

Differential Revision: https://reviews.llvm.org/D30510

llvm-svn: 297190