Add u-boot,dm-pre-reloc properties for uart pinmux configuration
nodes, which enables UART as early as possible (before relocation).
Without this we miss almost the half of output (U-boot version,
CPU defails, Reset cause, DRAM details etc.).
Fixes: cd69e8ef9b ("colibri-imx6ull: migrate pinctrl and regulators to dtb/dm")
Reviewed-by: Oleksandr Suvorov
Reviewed-by: Fabio Estevam
Signed-off-by: Igor Opaniuk