Convert CONFIG_AT91SAM9G20EK et al to Kconfig

This converts the following to Kconfig:
   CONFIG_AT91SAM9G20EK
   CONFIG_AT91SAM9260EK
   CONFIG_AT91SAM9G20EK_2MMC

Cc: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/atmel/at91sam9260ek/Kconfig b/board/atmel/at91sam9260ek/Kconfig
index 3844f08..40db313 100644
--- a/board/atmel/at91sam9260ek/Kconfig
+++ b/board/atmel/at91sam9260ek/Kconfig
@@ -9,4 +9,19 @@
 config SYS_CONFIG_NAME
 	default "at91sam9260ek"
 
+choice
+	prompt "Evaluation board"
+
+config AT91SAM9G20EK
+	bool "Atmel AT91SAM9G20 EK"
+
+config AT91SAM9260EK
+	bool "Atmel AT91SAM9260 EK"
+
+endchoice
+
+config AT91SAM9G20EK_2MMC
+	bool "Atmel AT91SAM9G20 EK 2MMC variant"
+	depends on AT91SAM9260EK
+
 endif