rockchip: dts: rk3399-u-boot: Add u-boot, dm-pre-reloc for spi1

Add u-boot,dm-pre-reloc property for spi1, so-that the
subsequent rk3399 boards which boot from SPI.

This help to separate the u-boot specific properties away
from base dts files so-that the Linux sync become easy and
meaningful.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>