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/etamin_defconfig b/configs/etamin_defconfig
index 5efadb8..65bdcf6 100644
--- a/configs/etamin_defconfig
+++ b/configs/etamin_defconfig
@@ -90,6 +90,8 @@
 CONFIG_SYS_NAND_PAGE_COUNT=0x80
 CONFIG_SYS_NAND_PAGE_SIZE=0x1000
 CONFIG_SYS_NAND_OOBSIZE=0xe0
+CONFIG_SYS_NAND_U_BOOT_LOCATIONS=y
+CONFIG_SYS_NAND_U_BOOT_OFFS=0x200000
 CONFIG_DM_SPI_FLASH=y
 CONFIG_SPI_FLASH_WINBOND=y
 CONFIG_MTD_UBI_FASTMAP=y