python: remove "earlycon" linux option from LupV board

This option doesn't work and triggers a warning by Linux when booting.

To make it work, we need a chosen node containing an `stdout-path`
property in the FDT which currently doesn't exist.

I tried to create via a couple of approaches it but encountered multiple
issues:

1. One can set `stdout-path` to the complete path of the tty device, but
   such path is impossible to get programmatically (unless it's
   hardcoded).
2. One can set `stdout-path` as a reference to a label. While labels are
   possible to generate easily, reference to labels cannot be generated
   with the current FDT library.

So just remove this option for the time being.

Change-Id: I58ad879c0fdf567a812069ae91ebc7d4f8accf13
Signed-off-by: Joël Porquet-Lupine <joel@porquet.org>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/61534
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>

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

@@ -514,7 +514,7 @@ class LupvBoard(AbstractSystemBoard, KernelDiskWorkload):
 
     @overrides(KernelDiskWorkload)
     def get_default_kernel_args(self) -> List[str]:
-        return ["earlycon console=ttyLIO0", "root={root_value}", "ro"]
+        return ["console=ttyLIO0", "root={root_value}", "ro"]
 
     @overrides(KernelDiskWorkload)
     def get_disk_device(self) -> str: