The Witherspoon has 3 LEDs connected to a PCA9552. Add them.
The names and reset values are taken from:
https://github.com/open-power/witherspoon-xml/blob/master/witherspoon.xml



Example booting obmc-phosphor-image:

  $ qemu-system-arm -M witherspoon-bmc -trace led_change_intensity
  1592693373.997015:led_change_intensity LED desc:'front-fault-4' color:green intensity 0% -> 100%
  1592693373.997632:led_change_intensity LED desc:'front-power-3' color:green intensity 0% -> 100%
  1592693373.998239:led_change_intensity LED desc:'front-id-5' color:green intensity 0% -> 100%
  1592693500.291805:led_change_intensity LED desc:'front-power-3' color:green intensity 100% -> 0%
  1592693500.312041:led_change_intensity LED desc:'front-power-3' color:green intensity 0% -> 100%
  1592693500.821254:led_change_intensity LED desc:'front-power-3' color:green intensity 100% -> 0%
  1592693501.331517:led_change_intensity LED desc:'front-power-3' color:green intensity 0% -> 100%
  1592693501.841367:led_change_intensity LED desc:'front-power-3' color:green intensity 100% -> 0%
  1592693502.350839:led_change_intensity LED desc:'front-power-3' color:green intensity 0% -> 100%
  1592693502.861134:led_change_intensity LED desc:'front-power-3' color:green intensity 100% -> 0%
  1592693503.371090:led_change_intensity LED desc:'front-power-3' color:green intensity 0% -> 100%

We notice the front-power LED starts to blink at a ~2Hz rate.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Luc Michel <luc.michel@greensocs.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20200912134041.946260-5-f4bug@amsat.org>