dev: Scrub out some lingering uses of MemObject.

MemObject doesn't do anything any more, and is basically just an alias
for ClockedObject.

Change-Id: Ic0e1658609e4e1d7f4b829fbc421f222e4869dee
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/20719
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

arch, cpu, dev, gpu, mem, sim, python: start using getPort.

Replace the getMasterPort, getSlavePort, and getEthPort functions
with getPort, and remove extraneous mechanisms that are no longer
necessary.

Change-Id: Iab7e3c02d2f3a0cf33e7e824e18c28646b5bc318
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/17040
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

learning_gem5: Adds the simple MemObject code

Adding more code from Learning gem5 Part II

See http://learning.gem5.org/book/part2/memoryobject.html

Change-Id: Iaa9480c5cdbe4090364f02e81dc1d0a0ddac392a
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/5022
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>