aarch64: Add SME runtime support

aarch64: Add SME runtime support

The runtime support routines for the call ABI of the Scalable Matrix
Extension (SME) are mostly in libgcc. Since libc.so cannot depend on
libgcc_s.so have an implementation of __arm_za_disable in libc for
libc internal use in longjmp and similar APIs.

__libc_arm_za_disable follows the same PCS rules as __arm_za_disable,
but it's a hidden symbol so it does not need variant PCS marking.

Using __libc_fatal instead of abort because it can print a message and
works in ld.so too. But for now we don't need SME routines in ld.so.

To check the SME HWCAP in asm, we need the _dl_hwcap2 member offset in
_rtld_global_ro in the shared libc.so, while in libc.a the _dl_hwcap2
object is accessed.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>