x86: add is_errata100 helper to fault_32|64.c

Further towards unifying these files, add another helper
in same spirit as is_errata93.

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>