Add aarch64 configurations

Add aarch64 configurations

This updates the sublibrary makefiles to use the appropiate
sourcefiles for aarch64.

It also removes the aarch64 source file for `__set_thread_area` from
the thread sublibrary makefile, as it is provided by lib-muslglue.

Signed-off-by: Robert Kuban <robert.kuban@opensynergy.com>
Reviewed-by: Eduard Vintilă <eduard.vintila47@gmail.com>
Reviewed-by: Razvan Virtan <virtanrazvan@gmail.com>
Reviewed-by: Razvan Deaconescu <razvand@unikraft.io>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #7