tls: move more details about initialization to arch

the thread_control_block structure needs to be different
between x64 and AArch64;
For AArch64's implementation for local execution, try to
match the layout in glibc and the generated code.

Do not align .tdata and .tbss sections with .tdata : ALIGN(64)
or it will affect the TLS loads.

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
Cc: Glauber Costa <glommer@cloudius-systems.com>
Cc: Will Newton <will.newton@linaro.org>
Signed-off-by: Avi Kivity <avi@cloudius-systems.com>