perf: Force architectures to opt-in to guest callbacks

Introduce GUEST_PERF_EVENTS and require architectures to select it to
allow registering and using guest callbacks in perf.  This will hopefully
make it more difficult for new architectures to add useless "support" for
guest callbacks, e.g. via copy+paste.

Stubbing out the helpers has the happy bonus of avoiding a load of
perf_guest_cbs when GUEST_PERF_EVENTS=n on arm64/x86.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20211111020738.2512932-9-seanjc@google.com
diff --git a/init/Kconfig b/init/Kconfig
index 036b750..72d40b3 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1804,6 +1804,10 @@
 	help
 	  See tools/perf/design.txt for details.
 
+config GUEST_PERF_EVENTS
+	bool
+	depends on HAVE_PERF_EVENTS
+
 config PERF_USE_VMALLOC
 	bool
 	help