at91: reworked support for meesc board

The meesc board support was broken. Within this opportunity, I completely
reworked the board files.

Signed-off-by: Daniel Gorsulowski <Daniel.Gorsulowski@esd.eu>

boards.cfg

@@ -86,7 +86,8 @@ cpu9G20_128M                 arm         arm926ejs   cpu9260             eukrea
 cpu9G20_nand_128M            arm         arm926ejs   cpu9260             eukrea         at91        cpu9260:CPU9G20,CPU9G20_128M,NANDBOOT
 top9000eval_xe               arm         arm926ejs   top9000             emk            at91        top9000:EVAL9000
 top9000su_xe                 arm         arm926ejs   top9000             emk            at91        top9000:SU9000
-meesc                        arm         arm926ejs   -                   esd            at91
+meesc                        arm         arm926ejs   meesc               esd            at91        meesc:AT91SAM9263,SYS_USE_NANDFLASH
+meesc_dataflash              arm         arm926ejs   meesc               esd            at91        meesc:AT91SAM9263,SYS_USE_DATAFLASH
 otc570                       arm         arm926ejs   -                   esd            at91
 pm9261                       arm         arm926ejs   -                   ronetix        at91
 pm9263                       arm         arm926ejs   -                   ronetix        at91