at91rm9200ek: convert to at91

This patch removes some functionality from at91rm9200ek board but the
remaining functionality does now work with newer at91 code and
arm-relocation.

Currently missing features are:
 - dataflash booting (due to missing HW for testing)
 - MMC/SD-Card
 - first stage bootloader support is completely removed (not needed for
   NOR)

Cause this board was (some days ago) reference for all at91rm9200 based
boards this should be a good starting point to convert all remaining
at91rm9200 borads to at91 code. Aside from that this is a good base to
get some drivers between at91sam/at91rm/avr32 merged.

Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
Signed-off-by: Reinhard Meyer <u-boot@emk-elektronik.de>