Remove isTlsLocalDynamicRel and isTlsInitialExecRel.

This feels a bit hackish, but I think it is still an improvement.

The way a tls address is computed in the various architectures is not
that different. For example, for local dynamic we need the base of the
tls (R_TLSLD or R_TLSLD_PC), and the offset of that particular symbol
(R_ABS).

Given the similarity, we can just use the expressions instead of
having two additional target hooks.

llvm-svn: 302279