mem: Minimize the use of MemObject.

MemObject doesn't provide anything beyond its base ClockedObject any
more, so this change removes it from most inheritance hierarchies.
Occasionally MemObject is replaced with SimObject when I was fairly
confident that the extra functionality of ClockedObject wasn't needed.

Change-Id: Ic014ab61e56402e62548e8c831eb16e26523fdce
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18289
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Anthony Gutierrez <anthony.gutierrez@amd.com>
Maintainer: Gabe Black <gabeblack@google.com>

python: Don't assume SimObjects live in the global namespace

The importer in Python 3 doesn't like the way we import SimObjects
from the global namespace. Convert the existing SimObject declarations
to import from m5.objects. As a side-effect, this makes these files
consistent with configuration files.

Change-Id: I11153502b430822130722839e1fa767b82a027aa
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/15981
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>

mem: different HMC configuration

In this new hmc configuration we have used the existing components in gem5
mainly [SerialLink] [NoncoherentXbar]& [DRAMCtrl] to define 3 different
architecture for HMC.

Highlights

1- It explores 3 different HMC architectures

2- It creates 4-HMC crossbars and attaches 16 vault controllers with it.
This will connect vaults to serial links

3- From the previous version, HMCController with round robin funtionality
is being removed and all the serial links are being accessible directly
from user ports

4- Latency incorporated by HMCController (in previous version) is being
added to SerialLink

Committed by Jason Lowe-Power <jason@lowepower.com>

mem: hmc: serial link model

This changeset adds a serial link model for the Hybrid Memory Cube (HMC).
SerialLink is a simple variation of the Bridge class, with the ability to
account for the latency of packet serialization. Also trySendTiming has been
modified to correctly model bandwidth.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>