AT91: at91sam9g20ek: merge 2mmc version in one board

The board-sam9g20ek-2slot-mmc.c was a revision of the at91sam9g20ek
since board revision C. It contains 2 sd/mmc slots.

This merge keep the support of the old machine ID
MACH_AT91SAM9G20EK_2MMC for backward compatibility.

Now we use the ATAG to pass the hardware functionality to kernel
with this board revision encoding
 bit 0:
     0 => 1 sd/mmc slot
     1 => 2 sd/mmc slots connectors (board from revision C)

system_rev tested on Barebox commit d8f3ee103a9f4bd

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
diff --git a/arch/arm/mach-at91/Kconfig b/arch/arm/mach-at91/Kconfig
index 7b6ae6d..23bf5c2c 100644
--- a/arch/arm/mach-at91/Kconfig
+++ b/arch/arm/mach-at91/Kconfig
@@ -338,6 +338,7 @@
 	  that embeds only one SD/MMC slot.
 
 config MACH_AT91SAM9G20EK_2MMC
+	depends on MACH_AT91SAM9G20EK
 	bool "Atmel AT91SAM9G20-EK Evaluation Kit with 2 SD/MMC Slots"
 	select HAVE_NAND_ATMEL_BUSWIDTH_16
 	help