x86/mce: Take action on UCNA/Deferred errors again

Commit

  fa92c586 ("x86, mce: Support memory error recovery for both UCNA
		and Deferred error in machine_check_poll")

added handling of UCNA and Deferred errors by adding them to the ring
for SRAO errors.

Later, commit

  fd4cf79f ("x86/mce: Remove the MCE ring for Action Optional errors")

switched storage from the SRAO ring to the unified pool that is still
in use today. In order to only act on the intended errors, a filter
for MCE_AO_SEVERITY is used -- effectively removing handling of
UCNA/Deferred errors again.

Extend the severity filter to include UCNA/Deferred errors again.
Also, generalize the naming of the notifier from SRAO to UC to capture
the extended scope.

Note, that this change may cause a message like the following to appear,
as the same address may be reported as SRAO and as UCNA:

 Memory failure: 0x5fe3284: already hardware poisoned

Technically, this is a return to previous behavior.

Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20200103150722.20313-2-jschoenh@amazon.de