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/devkit3250_defconfig b/configs/devkit3250_defconfig
index dc85a84..8f98fc5 100644
--- a/configs/devkit3250_defconfig
+++ b/configs/devkit3250_defconfig
@@ -58,6 +58,8 @@
 CONFIG_SYS_NAND_PAGE_SIZE=0x800
 CONFIG_SYS_NAND_OOBSIZE=0x40
 # CONFIG_SYS_NAND_5_ADDR_CYCLE is not set
+CONFIG_SYS_NAND_U_BOOT_LOCATIONS=y
+CONFIG_SYS_NAND_U_BOOT_OFFS=0x40000
 CONFIG_PHYLIB=y
 CONFIG_PHY_ADDR_ENABLE=y
 CONFIG_PHY_ADDR=31