configs: Add missing _pre_instantiate call in "run_lupv.py"

As of this change:
https://gem5-review.googlesource.com/c/public/gem5/+/65051, the
`_pre_instantiate` function must be called prior to `m5.instantiate`
when using the stdlib without the Simulator module.

Change-Id: Id5cec3b643d556b0f742719596abb53533b84cbd
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/65871
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>

configs/example/lupv/run_lupv.py

@@ -107,6 +107,7 @@ board.set_kernel_disk_workload(
 print("Running with ISA: " + processor.get_isa().name)
 print()
 root = Root(full_system=True, system=board)
+board._pre_instantiate()
 m5.instantiate()
 print("Beginning simulation!")