avr32: stk1002 and ngw100 convergence

avr32: stk1002 and ngw100 convergence

Make STK1002 and NGW100 boards act more alike:
  - STK boards can use as many arguments as NGW
  - STK boards don't need to manage FPGAs either
  - NGW commands should match STK ones

Also spell U-Boot right in prompts for STK1002 and NGW100.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
[haavard.skinnemoen@atmel.com: update STK100[34] as well]
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>