ARM: dts: ipq4019: Add a default chosen node

Add a 'chosen' node to select the serial console.
This is needed when bootloaders do not pass the
'console=' bootargs.

Acked-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Sricharan R <sricharan@codeaurora.org>
Signed-off-by: Andy Gross <andy.gross@linaro.org>