x86/mce/AMD: Reduce number of blocks scanned per bank

From Fam17h onwards, the number of extended MCx_MISC register blocks is
reduced to 4. It is an architectural change from what we had on
earlier processors.

Although theoritically the total number of extended MCx_MISC
registers was 8 in earlier processor families, in practice we
only had to use the extra registers for MC4. And only 2 of those
were used. So this change does not affect older processors.
Tested on Fam10h and Fam15h systems.

Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/1453750913-4781-6-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>