kernel/watchdog: fix Kconfig constraints for perf hardlockup watchdog

kernel/watchdog: fix Kconfig constraints for perf hardlockup watchdog

Commit 05a4a9527931 ("kernel/watchdog: split up config options") lost
the perf-based hardlockup detector's dependency on PERF_EVENTS, which
can result in broken builds with some powerpc configurations.

Restore the dependency.  Add it in for x86 too, despite x86 always
selecting PERF_EVENTS it seems reasonable to make the dependency
explicit.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: 05a4a9527931 ("kernel/watchdog: split up config options")
Signed-off-by: Nicholas Piggin <[email protected]>
Acked-by: Don Zickus <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>