mem: Replace EventWrapper in PacketQueue with EventFunctionWrapper

mem: Replace EventWrapper in PacketQueue with EventFunctionWrapper

In order to replicate the same `name()` output with `PacketQueue`, subclasses
using EventFunctionWrapper must initialize PacketQueue with their own name so
the sendEvent holds the name of the subclass.

Change-Id: Ib091e118bab8858192e1d1370d61def42958ec29
Signed-off-by: Sean Wilson <spwilson2@wisc.edu>
Reviewed-on: https://gem5-review.googlesource.com/3744
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>