x86: use v8086_mode helper, trivial unification

Use v8086_mode inline in fault_32.c, no functional change
also ifdef the section for 32-bit only and add to fault_64.c

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>