dev, arm: Add a flag to enable/disable gem5 GIC extensions

Make it possible to disable gem5 gic extensions by setting the
gem5_extensions param to False from Python.

Change-Id: Icb255105925ef49891d69cc9fe5cc55578ca066d
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Geoffrey Blake <geoffrey.blake@arm.com>
3 files changed