configs: Add GPUFS --root-partition option

Different GPUFS disk images have different root partitions that Linux
needs to boot from. In particular, Ubuntu's new installer has a GRUB
partition that cannot seem to be removed. Adding this as an option
prevents needing to edit a config script to change one character each
time a different disk image is used.

Change-Id: Iac2996ea096047281891a70aa2901401ac9746fc
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/71918
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>

configs/example/gpufs/runfs.py

@@ -151,6 +151,13 @@ def addRunFSOptions(parser):
         help="Exit simulation after running this many kernels",
     )
 
+    parser.add_argument(
+        "--root-partition",
+        type=str,
+        default="/dev/sda1",
+        help="Root partition of disk image",
+    )
+
 
 def runGpuFSSystem(args):
     """

configs/example/gpufs/system/system.py

@@ -50,7 +50,7 @@ def makeGpuFSSystem(args):
         "earlyprintk=ttyS0",
         "console=ttyS0,9600",
         "lpj=7999923",
-        "root=/dev/sda1",
+        f"root={args.root_partition}",
         "drm_kms_helper.fbdev_emulation=0",
         "modprobe.blacklist=amdgpu",
         "modprobe.blacklist=psmouse",