tests/functional: Convert Aspeed arm SDK tests

tests/functional: Convert Aspeed arm SDK tests

Drop the SSH connection which was introduced in the avocado tests to
workaround read issues when interacting with console.

EXTRA_BOOTARGS was introduced to reduce the console output at Linux
boot time. This didn't have the desired effect as we still had issues
when trying to match patterns on the console and we had to use the ssh
connection as a workaround.

While at it, remove the U-Boot EXTRA_BOOTARGS variable which has
become useless.

Signed-off-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20241122090322.1934697-3-clg@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>