KVM: selftests: Fixup config fragment for access_tracking_perf_test

access_tracking_perf_test requires CONFIG_IDLE_PAGE_TRACKING. However
this is missing from the config fragment, so add it in so that this test
is no longer skipped.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230308110948.1820163-2-ryan.roberts@arm.com