at91: Convert remaining boards to new-style UART initialization

Convert the following AT91RM9200-based boards to the new-style UART
initialization:
  - Ajeco 1ARM Single Board Computer
  - Sperry-Sun KAFA board
  - picotux 200

Remove the deprecated at91_init_serial

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Andrew Victor <linux@maxim.org.za>