Use the AbstractMem's new getBackdoor call to implement the recvAtomicBackdoor call in the memory controller's port. Change-Id: I10a7d22edb62afc3b77a2d462f297572c04f020d Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/36978 Maintainer: Gabe Black <gabe.black@gmail.com> Reviewed-by: Jason Lowe-Power <power.jg@gmail.com> Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br> Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com> Tested-by: kokoro <noreply+kokoro@google.com>