KVM: selftests: Add CONFIG_EVENTFD for irqfd selftest

In 7e9b231 ("KVM: selftests: Add a KVM_IRQFD test to verify
uniqueness requirements") we added a test for the newly added irqfd
support but since this feature works with eventfds it won't work unless
the kernel has been built wth eventfd support.  Add CONFIG_EVENTFD to
the list of required options for the KVM selftests.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250710-kvm-selftests-eventfd-config-v1-1-78c276e4b80f@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: broonie

tools/testing/selftests/kvm/config

@@ -1,5 +1,6 @@
 CONFIG_KVM=y
 CONFIG_KVM_INTEL=y
 CONFIG_KVM_AMD=y
+CONFIG_EVENTFD=y
 CONFIG_USERFAULTFD=y
 CONFIG_IDLE_PAGE_TRACKING=y