learning-gem5: Fix missing misc.hh in hello_object.cc

misc.hh has been renamed in
commit 1088f0c4ac3999fc3c363cc51daef4cfb360a2bd

Change-Id: Ic4f8c6423e6a5466f8d924e793a24f62bb4eca9c
Reviewed-on: https://gem5-review.googlesource.com/6361
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

learning_gem5: Add code for hello-goodbye example

Adding more code from Learning gem5 Part II

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

Change-Id: I9fe5655239e011c718c5cf5fd62bebcda66ea966
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/5021
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>