stdlib: Change the default kernel boot param from "ro" to "rw"

Running workloads likely causes some content to be written to
the disk image, e.g., `m5 readfile`. However, on riscv boards,
the default kernel param specifies the disk image to be read-only.

This change changes this param so that the disk image is
read-write by default.

Change-Id: I414e483ad11d747f34433560e32a8f91a425ce7e
Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/65194
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/gem5/components/boards/experimental/lupv_board.py

@@ -536,7 +536,7 @@ class LupvBoard(AbstractSystemBoard, KernelDiskWorkload):
 
     @overrides(KernelDiskWorkload)
     def get_default_kernel_args(self) -> List[str]:
-        return ["console=ttyLIO0", "root={root_value}", "ro"]
+        return ["console=ttyLIO0", "root={root_value}", "rw"]
 
     @overrides(KernelDiskWorkload)
     def get_disk_device(self) -> str:

src/python/gem5/components/boards/riscv_board.py

@@ -494,4 +494,4 @@ class RiscvBoard(AbstractSystemBoard, KernelDiskWorkload):
 
     @overrides(KernelDiskWorkload)
     def get_default_kernel_args(self) -> List[str]:
-        return ["console=ttyS0", "root={root_value}", "ro"]
+        return ["console=ttyS0", "root={root_value}", "rw"]

src/python/gem5/prebuilt/riscvmatched/riscvmatched_board.py

@@ -566,7 +566,7 @@ class RISCVMatchedBoard(
 
     @overrides(KernelDiskWorkload)
     def get_default_kernel_args(self) -> List[str]:
-        return ["console=ttyS0", "root={root_value}", "ro"]
+        return ["console=ttyS0", "root={root_value}", "rw"]
 
     @overrides(KernelDiskWorkload)
     def set_kernel_disk_workload(