x86: introduce __die helper to X86_32

Small step towards unifying traps_32|64.c.  No functional
changes.  Pull out a small helper from an if() statement
in die().

Marked as __kprobes as eventually we will want to call this
from do_page_fault similar to how X86_64 does it.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>