x86_64: Fix to keep watchdog disabled by default for i386/x86_64

x86_64: Fix to keep watchdog disabled by default for i386/x86_64

Fixed wrong expression which enabled watchdogs even if nmi_watchdog kernel
parameter wasn't set. This regression got slightly introduced with commit
b7471c6da94d30d3deadc55986cc38d1ff57f9ca.

Introduced NMI_DISABLED (-1) which allows to switch the value of NMI_DEFAULT
without breaking the APIC NMI watchdog code (again).

Fixes:
   https://bugzilla.novell.com/show_bug.cgi?id=298084
   http://bugzilla.kernel.org/show_bug.cgi?id=7839
And likely some more nmi_watchdog=0 related issues.

Signed-off-by: Daniel Gollub <dgollub@suse.de>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>