signal/x86/traps: Factor out show_signal

The code for conditionally printing unhanded signals is duplicated twice
in arch/x86/kernel/traps.c.  Factor it out into it's own subroutine
called show_signal to make the code clearer and easier to maintain.

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>