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/configs/sam9x60ek_qspiflash_defconfig b/configs/sam9x60ek_qspiflash_defconfig
index bc30c4c..b0f74e6 100644
--- a/configs/sam9x60ek_qspiflash_defconfig
+++ b/configs/sam9x60ek_qspiflash_defconfig
@@ -5,6 +5,7 @@
 CONFIG_SYS_MALLOC_LEN=0x81000
 CONFIG_SYS_MALLOC_F_LEN=0x8000
 CONFIG_TARGET_SAM9X60EK=y
+CONFIG_ATMEL_LEGACY=y
 CONFIG_NR_DRAM_BANKS=8
 CONFIG_ENV_SECT_SIZE=0x1000
 CONFIG_DM_GPIO=y