arm: kirkwood: Enable bootstd for Sheevaplug board

Enable bootstd for Sheevaplug board.
Remove JFFS2 support. See JFFS2 Vulnerability[1].
Enable LTO to keep board size within limit.
Move default envs to text-base environment

[1] https://lore.kernel.org/u-boot/20241114233005.GN3600562@bill-the-cat/T/#m2fc25da1d2c019bc3cd8676991fdd64b8a21aa9b

Signed-off-by: Tony Dinh <mibodhi@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
3 files changed