x86: add IRQ context simulation in module mce-inject

mce-inject provides a mechanism to simulate errors so that test
scripts can check for correct operation of the kernel without
requiring any specialized hardware to create rare events.

The existing code can simulate events in normal process context
and also in NMI context - but not in IRQ context. This patch
fills that gap.

Link: https://lkml.org/lkml/2011/12/7/537
Signed-off-by: Chen Gong <gong.chen@linux.intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>