u-boot: wakeup reasons back for GTA02

[Werner Almesberger]

So far, GTA02 didn't care about the wakeup reason, but just proceeded to
check for the boot menu. This means that the slightest touch of the POWER
button would turn it on.

I've now updated the corresponding GTA01 code for GTA02. Note that the
user experience may still be a little rough. I'll smooth this later.

(First, there's an interesting regression to fix - seems that something
I did recently broke the serial console in u-boot :-( )

- Werner

----------------------------------- Changes -----------------------------------

This ports wake-up reason handling forward from GTA01. In particular, it makes 
sure that we don't power up unless the POWER button is held down for a while.

The user interaction of all this still needs a bit of fine-tuning.

uboot-gta02.patch:
- board/neo1973/gta02/gta02.c (board_late_init): enabled wake-up reason
  handling and updated it for the PCF50633
gta02-bootmenu.patch: updated context for above change
nor-bootmenu.patch: 
- updated context
- board/neo1973/gta02/gta02.c (board_late_init): examine wakeup reason also on
  NOR boot