arm: add (default) config for nanopi2 board

Changes in relation to FriendlyARM's U-Boot nanopi2-v2016.01:
- Configuration changed, mainly several "CONFIG_..." moved from
  s5p4418_nanopi2.h to s5p4418_nanopi2_defconfig and USB related
  configs removed because USB is not supported yet.
- s5p4418_nanopi2.h: "CONFIG_" removed from several s5p4418/nanopi2
  specific defines because the appropriate values do not need to be
  configurable.
- pinctrl is supported now, therefore "CONFIG_PINCTRL=y" added to
  s5p4418_nanopi2_defconfig.

Signed-off-by: Stefan Bosch <stefan_b@posteo.net>