Convert CONFIG_SYS_FLASH_EMPTY_INFO to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_FLASH_EMPTY_INFO

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/ls1021atwr_nor_lpuart_defconfig b/configs/ls1021atwr_nor_lpuart_defconfig
index 82e3b39..99271e7 100644
--- a/configs/ls1021atwr_nor_lpuart_defconfig
+++ b/configs/ls1021atwr_nor_lpuart_defconfig
@@ -68,6 +68,7 @@
 CONFIG_FLASH_CFI_DRIVER=y
 CONFIG_CFI_FLASH_USE_WEAK_ACCESSORS=y
 CONFIG_SYS_FLASH_USE_BUFFER_WRITE=y
+CONFIG_SYS_FLASH_EMPTY_INFO=y
 CONFIG_SYS_FLASH_CFI=y
 CONFIG_PHY_ATHEROS=y
 CONFIG_DM_ETH=y