power: pmic: rk8xx: Fix power-on source check in SPL

The commit 30975fb7 ("rockchip: Add option to prevent booting on
power plug-in") introduce an option to prevent booting a device when the
device was powered on due to power plug-in instead of pressing a power
button.

This feature works by checking the power-on source during PMIC probe
and powers off the device if power-on source was power plug-in.
This check currently runs very late at PMIC probe in U-Boot proper.

Fix so that the power-on source check can work at probe time in SPL.
Also enable probe after bind and remove the PMIC banner in SPL.

With this we can use ROCKCHIP_RK8XX_DISABLE_BOOT_ON_POWERON and
SPL_PMIC_RK8XX to power off the device very quickly after TPL instead
of after TF-A and U-Boot proper has been loaded and run.

  DDR V1.18 f366f69a7d typ 23/07/17-15:48:58
  ln
  LP4/4x derate en, other dram:1x trefi
  ddrconfig:7
  LPDDR4X, 324MHz
  BW=32 Col=10 Bk=8 CS0 Row=17 CS1 Row=17 CS=2 Die BW=16 Size=8192MB

  change to: 324MHz
  clk skew:0x64

  change to: 528MHz
  clk skew:0x58

  change to: 780MHz
  clk skew:0x58

  change to: 1056MHz(final freq)
  clk skew:0x40
  out
  Power Off due to plug-in event

Fixes: 30975fb7 ("rockchip: Add option to prevent booting on power plug-in")
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>