signal/arc: Push siginfo generation into unhandled_exception

Pass signr, sicode, and address into unhandled_exception as explicit
parameters instead of members of struct siginfo.  Then in unhandled
exception generate and send the siginfo using force_sig_fault.

This keeps the code simpler and less error prone.

Acked-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>