x86/mce: Add a struct mce.kflags field

There can be many different subsystems register on the mce handler
chain. Add a new bitmask field and define values so that handlers can
indicate whether they took any action to log or otherwise handle an
error.

The default handler at the end of the chain can use this information to
decide whether to print to the console log.

Boris suggested a generic name and leaving plenty of spare bits for
possible future use.

 [ bp: Move flag bits to the internal mce.h header and use BIT_ULL(). ]

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/20200214222720.13168-4-tony.luck@intel.com