Convert CONFIG_ATMEL_LEGACY to Kconfig

This converts the following to Kconfig:
   CONFIG_ATMEL_LEGACY

Cc: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/arch/arm/mach-at91/Kconfig b/arch/arm/mach-at91/Kconfig
index 79fe87c..fc193b9 100644
--- a/arch/arm/mach-at91/Kconfig
+++ b/arch/arm/mach-at91/Kconfig
@@ -315,6 +315,9 @@
 	bool "Keep pullups on peripheral pins"
 	depends on CPU_ARM926EJS
 
+config ATMEL_LEGACY
+	bool "Legacy GPIO support"
+
 source "board/atmel/at91sam9260ek/Kconfig"
 source "board/atmel/at91sam9261ek/Kconfig"
 source "board/atmel/at91sam9263ek/Kconfig"