rockchip: Fix early use of bootph props

Running U-Boot on a ROCK 3 Model A result in the following:

  No serial driver found
  resetting ...
  no sysreset
  ### ERROR ### Please RESET the board ###

Replace bootph- props with u-boot,dm- props to fix this.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>