meson: merge hw_common_arch in target_common_system_arch

meson: merge hw_common_arch in target_common_system_arch

No need to keep two different libraries, as both are compiled with exact
same flags. As well, rename target common libraries to common_{arch} and
system_{arch}, to follow what exists for common and system libraries.

Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/r/20250521223414.248276-8-pierrick.bouvier@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>