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/P5040DS_SDCARD_defconfig b/configs/P5040DS_SDCARD_defconfig
index bf72874..48e3ffa 100644
--- a/configs/P5040DS_SDCARD_defconfig
+++ b/configs/P5040DS_SDCARD_defconfig
@@ -75,6 +75,7 @@
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_FLASH_CFI_DRIVER=y
 CONFIG_SYS_FLASH_USE_BUFFER_WRITE=y
+CONFIG_SYS_FLASH_EMPTY_INFO=y
 CONFIG_SYS_FLASH_CFI=y
 CONFIG_SYS_MAX_FLASH_BANKS=2
 CONFIG_DM_SPI_FLASH=y