arch: arm: dts: ls1046a: tag serial nodes with bootph-all

Make sure the serial driver is initialized before relocation by tagging
the serial nodes with "bootph-all".

In order to keep the serial nodes in sync with their representation in
the Linux dts, add these u-boot specific properties to *-u-boot.dtsi
files.

Signed-off-by: Camelia Groza <camelia.groza@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>