[AArch64] Allow -mattr=tpidr-el[1|2|3]

Added subtarget features for AArch64 to use TPIDR_EL[1|2|3] as the TLS base
register, rather than the default TPIDR_EL0.

Patch by Philip Derrin!

Differential revision: https://reviews.llvm.org/D54685



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356657 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed