at91rm9200ek: add configure target for RAM boot

This patch also removes now unnecessary config.mk in board directory and
make usage of new features in boards.cfg.

Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
diff --git a/boards.cfg b/boards.cfg
index 319c812..b04ba40 100644
--- a/boards.cfg
+++ b/boards.cfg
@@ -48,7 +48,8 @@
 SMN42                        arm         arm720t     -                   siemens        lpc2292
 evb4510                      arm         arm720t     -                   -              s3c4510b
 a320evb                      arm         arm920t     -                   faraday        a320
-at91rm9200ek                 arm         arm920t     -                   atmel          at91
+at91rm9200ek                 arm         arm920t     at91rm9200ek        atmel          at91        at91rm9200ek
+at91rm9200ek_ram             arm         arm920t     at91rm9200ek        atmel          at91        at91rm9200ek:RAMBOOT
 eb_cpux9k2                   arm         arm920t     -                   BuS            at91
 cmc_pu2                      arm         arm920t     -                   -              at91rm9200
 csb637                       arm         arm920t     -                   -              at91rm9200