scons: Break make_obj into make_static and make_shared functions.

scons: Break make_obj into make_static and make_shared functions.

The make_obj function took a boolean value which just selected which
of the two lines it in would actually do something. This change breaks
it into two lambdas, make_static and make_shared, which just do
whichever line would have been requested, making the funciton name more
self descriptive and getting rid of the generally unnamed and opaque
boolean argument.

Change-Id: I457e40034b7e7f5a3e7294a8e1f15bbd42e0720e
Reviewed-on: https://gem5-review.googlesource.com/5984
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>