x86/mce: Don't check for the overflow bit on action optional machine checks

We currently do not process SRAO (Software Recoverable Action Optional)
machine checks if they are logged with the overflow bit set to 1 in the
machine check bank status register. This is overly conservative.

There are two cases where we could end up with an SRAO+OVER log based
on the SDM volume 3 overwrite rules in "Table 15-8. Overwrite Rules for
UC, CE, and UCR Errors"

1) First a corrected error is logged, then the SRAO error overwrites.
   The second error overwrites the first because uncorrected errors
   have a higher severity than corrected errors.
2) The SRAO error was logged first, followed by a correcetd error.
   In this case the first error is retained in the bank.

So in either case the machine check bank will contain the address
of the SRAO error. So we can process that even if the overflow bit
was set.

Reported-by: Yongkai Wu <yongkaiwu@tencent.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190718182920.32621-1-tony.luck@intel.com