ARM: atmel: add at91sam9g20ek_2mmc nand boot support

Add at91sam9g20_2mmc nand boot support. on this board, there is no
dataflash, so disable it

change one commet for at91sam9g20ek board

Signed-off-by: Bo Shen <voice.shen@atmel.com>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>
diff --git a/boards.cfg b/boards.cfg
index b1319aa..32b0ccf 100644
--- a/boards.cfg
+++ b/boards.cfg
@@ -95,6 +95,7 @@
 at91sam9g20ek_dataflash_cs0  arm         arm926ejs   at91sam9260ek       atmel          at91        at91sam9260ek:AT91SAM9G20,SYS_USE_DATAFLASH_CS0
 at91sam9g20ek_dataflash_cs1  arm         arm926ejs   at91sam9260ek       atmel          at91        at91sam9260ek:AT91SAM9G20,SYS_USE_DATAFLASH_CS1
 at91sam9g20ek_nandflash      arm         arm926ejs   at91sam9260ek       atmel          at91        at91sam9260ek:AT91SAM9G20,SYS_USE_NANDFLASH
+at91sam9g20ek_2mmc_nandflash arm         arm926ejs   at91sam9260ek       atmel          at91        at91sam9260ek:AT91SAM9G20,AT91SAM9G20EK_2MMC,SYS_USE_NANDFLASH
 at91sam9m10g45ek_nandflash   arm         arm926ejs   at91sam9m10g45ek    atmel          at91        at91sam9m10g45ek:AT91SAM9M10G45,SYS_USE_NANDFLASH
 at91sam9rlek_dataflash       arm         arm926ejs   at91sam9rlek        atmel          at91        at91sam9rlek:AT91SAM9RL,SYS_USE_DATAFLASH
 at91sam9rlek_nandflash       arm         arm926ejs   at91sam9rlek        atmel          at91        at91sam9rlek:AT91SAM9RL,SYS_USE_NANDFLASH