x86, mce: Support specifying context for software mce injection

The cpu context is specified via the new mce.inject_flags fields.
This allows more realistic machine check testing in different
situations. "RANDOM" context is implemented via NMI broadcasting to
add randomization to testing.

AK: Fix NMI broadcasting check. Fix 32-bit building. Some race
fixes. Move to module. Various changes

ChangeLog:

v3:

- Re-based on latest x86-tip.git/mce4

- Fix 32-bit building

v2:

- Re-base on latest x86-tip.git/mce3

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>