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/am43xx_evm_defconfig b/configs/am43xx_evm_defconfig
index 380a35a..98cd6b4 100644
--- a/configs/am43xx_evm_defconfig
+++ b/configs/am43xx_evm_defconfig
@@ -65,6 +65,8 @@
 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=0x180000
 CONFIG_SF_DEFAULT_SPEED=48000000
 CONFIG_SPI_FLASH_MACRONIX=y
 CONFIG_PHY_GIGE=y