mem: Fix DRAM activationlLimit bug
mem: Fix DRAM activationlLimit bug

Ensure that we do the proper event scheduling also when the activation
limit is disabled.
(transplanted from 59f9f18aae0c2785beabe9085f13a8b20ae839da)

andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin