Internal TLS support for aarch64, x86_64, riscv, ppc64, and s390x

Internal TLS support for aarch64, x86_64, riscv, ppc64, and s390x

For each architecture, aarch64, x86_64, riscv, ppc64, and s390x,
this commit defines a suitable 'get_tls_dtv_addr' method and,
when necessary, a 'get_tls_dtp_offset' method.

It also registers svr4_tls_get_thread_local_address, defined in
svr4-tls-tdep.c (in an earlier commit), as the
get_thread_local_address gdbarch method.  It also registers its
architecture specific code using svr4_tls_register_tls_methods().

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=24548
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31563

Tested-By: Luis Machado <luis.machado@arm.com>
Approved-By: Luis Machado <luis.machado@arm.com>