x86/mce: Create helper function to save addr/misc when needed

The MCI_STATUS_MISCV and MCI_STATUS_ADDRV bits in the bank status
registers define whether the MISC and ADDR registers respectively
contain valid data - provide a helper function to check these bits
and read the registers when needed.

In addition, processors that support software error recovery (as
indicated by the MCG_SER_P bit in the MCG_CAP register) may include
some undefined bits in the ADDR register - mask these out.

Acked-by: Borislav Petkov <bp@amd64.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>