ANDROID: gki_defconfig: Enable CONFIG_VM_EVENT_COUNTERS

This was "default y" but disabled manually because we set
CONFIG_EXPERT=y. Disabling it does not seem to be a big win and we have
had requests to enable it.

Bug: 150871026
Change-Id: I4a7f8da1e8480dc46f168def89016a5152e421ea
Signed-off-by: Alistair Delva <adelva@google.com>