sim: Fix need to save address space info during serialization.

sim: Fix need to save address space info during serialization.

This fixes a fatal already mapped error in
FuncPageTable::allocate that occurs in some cases
when restoring from a checkpoint.

Change-Id: Ib726a69358118626663e42b7f14889b0d3a98de0
Reported-by: Ruohuang Zheng <zhengruohuang@gmail.com>
Signed-off-by: Austin Harris <austinharris@utexas.edu>
Reviewed-on: https://gem5-review.googlesource.com/5901
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>