[ELF/AArch64] Fix local TLS relocations

This patch fixes the R_AARCH64_TLSLE_ADD_TPREL_HI12 and R_AARCH64_TLSLE_ADD_TPREL_LO12_NC
handling by using the correct offset by using the target layout along with
aarch64 alignments requirements.

It fixes the TLS test-suite SingleSource failures for aarch64:

* SingleSource/UnitTests/Threads/2010-12-08-tls.execution_time
* SingleSource/UnitTests/Threads/tls.execution_time

llvm-svn: 238258