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/comtrend_wap5813n_ram_defconfig b/configs/comtrend_wap5813n_ram_defconfig
index b7174ff..dc0f7ce 100644
--- a/configs/comtrend_wap5813n_ram_defconfig
+++ b/configs/comtrend_wap5813n_ram_defconfig
@@ -51,6 +51,7 @@
 CONFIG_DM_MTD=y
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_CFI_FLASH=y
+CONFIG_SYS_FLASH_EMPTY_INFO=y
 CONFIG_SYS_FLASH_PROTECTION=y
 CONFIG_SYS_FLASH_CFI=y
 CONFIG_SYS_MAX_FLASH_BANKS_DETECT=y