x86/nmi_watchdog: Fix old-style NMI watchdog regression on old Intel CPUs

The following commit:

   3a4ac121 ("x86/perf: Add hardware performance events support for Zhaoxin CPU.")

Got the old-style NMI watchdog logic wrong and broke it for basically every
Intel CPU where it was active. Which is only truly old CPUs, so few people noticed.

On CPUs with perf events support we turn off the old-style NMI watchdog, so it
was pretty pointless to add the logic for X86_VENDOR_ZHAOXIN to begin with ... :-/

Anyway, the fix is to restore the old logic and add a 'break'.

[ mingo: Wrote a new changelog. ]

Fixes: 3a4ac121

 ("x86/perf: Add hardware performance events support for Zhaoxin CPU.")
Signed-off-by: CodyYao-oc <CodyYao-oc@zhaoxin.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210607025335.9643-1-CodyYao-oc@zhaoxin.com