Convert CONFIG_SYS_NAND_U_BOOT_LOCATIONS et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_NAND_U_BOOT_LOCATIONS
   CONFIG_SYS_NAND_U_BOOT_OFFS

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/sama5d4ek_nandflash_defconfig b/configs/sama5d4ek_nandflash_defconfig
index 7f02d46..c33187e 100644
--- a/configs/sama5d4ek_nandflash_defconfig
+++ b/configs/sama5d4ek_nandflash_defconfig
@@ -69,6 +69,8 @@
 CONFIG_SYS_NAND_PAGE_COUNT=0x40
 CONFIG_SYS_NAND_PAGE_SIZE=0x1000
 CONFIG_SYS_NAND_OOBSIZE=0xe0
+CONFIG_SYS_NAND_U_BOOT_LOCATIONS=y
+CONFIG_SYS_NAND_U_BOOT_OFFS=0x40000
 CONFIG_DM_SPI_FLASH=y
 CONFIG_SF_DEFAULT_SPEED=30000000
 CONFIG_SPI_FLASH_ATMEL=y