x86/mce: Update bootlog description to reflect behavior on AMD

The bootlog option is only disabled by default on AMD Fam10h and older
systems.

Update bootlog description to say this. Change the family value to hex
to avoid confusion.

Signed-off-by: Yazen Ghannam <yazen.ghannam@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/20170613162835.30750-9-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Documentation/x86/x86_64/boot-options.txt

@@ -36,7 +36,8 @@ Machine check
 		to broadcast MCEs.
    mce=bootlog
 		Enable logging of machine checks left over from booting.
-		Disabled by default on AMD because some BIOS leave bogus ones.
+		Disabled by default on AMD Fam10h and older because some BIOS
+		leave bogus ones.
 		If your BIOS doesn't do that it's a good idea to enable though
 		to make sure you log even machine check events that result
 		in a reboot. On Intel systems it is enabled by default.