Add arm64_force_sig_ptrace_errno_trap for consistency with
arm64_force_sig_fault and use it where appropriate.

This adds the show_signal logic to the force_sig_errno_trap case,
where it was apparently overlooked earlier.
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>