tegra: fdt: Ensure that the console UART is enabled

Many tegra boards have the console UART node disabled. With livetree this
prevents serial from working since it does not 'force' the console to be
bound. Updates the affected boards to fix this error.

The boards were checked with:

for b in $(grep  tegra boards.cfg  |grep -v integrator | \
		awk '{print $7}' | sort); do
	echo $b;
	fdtgrep -c nvidia,tegra20-uart b/$b/u-boot.dtb |grep okay;
done

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Tested-on: Beaver, Jetson-TK1