board: lsxl: make last resort recovery more reliable

If something is wrong with the environment, we cannot rely on a proper
u-boot operation anymore. In fact, it is possible, that we never reach
misc_init_r() with a broken environment.

Also don't enable the netconsole by environment settings. This way the
user don't have to reconfigure the environment. Instead the network
console is only enabled when the push button is pressed during boot.

Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Stefan Roese <sr@denx.de>