backends: Add aarch64 abi_cfi.

Setup initial CIE values for aarch64 for use with dwarf_frame functions.
Register info prefix should be the empty string (not NULL) when not used.
Add an EM_AARCH64 testcase to tests/run-addrcfi.sh to check both issues.

Signed-off-by: Mark Wielaard <mjw@redhat.com>
9 files changed