cpuat91: convert to new at91 soc architecture

convert the board to the new soc architecture
update default config
i2c upgrade taken from eb_cpux9k2.h & board/BuS/eb_cpux9k2/cpux9k2.c

Signed-off-by: Eric Bénard <eric@eukrea.com>
Signed-off-by: Reinhard Meyer <u-boot@emk-elektronik.de>