config: Make ex5_*.py independent of old configs

config: Make ex5_*.py independent of old configs

The ex5_LITTLE and ex5_big configs currently depend on Caches.py and
O3_ARM_v7a.py. These aren't actual dependencies since all of the
params from the caches and the old O3 model are overridden. This
changeset updates the ex5 models to derive from the base SimObjects
instead.

Change-Id: I999e73bb9cc21ad96865c1bc0dd5973faa48ab61
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Gabor Dozsa <gabor.dozsa@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/3942
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>