Convert CONFIG_SYS_MAX_FLASH_SECT to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_MAX_FLASH_SECT

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/ls1021atwr_nor_defconfig b/configs/ls1021atwr_nor_defconfig
index 4ee9fe1..7571d7c 100644
--- a/configs/ls1021atwr_nor_defconfig
+++ b/configs/ls1021atwr_nor_defconfig
@@ -70,6 +70,7 @@
 CONFIG_SYS_FLASH_USE_BUFFER_WRITE=y
 CONFIG_SYS_FLASH_EMPTY_INFO=y
 CONFIG_SYS_FLASH_CFI=y
+CONFIG_SYS_MAX_FLASH_SECT=1024
 CONFIG_PHY_ATHEROS=y
 CONFIG_DM_ETH=y
 CONFIG_DM_MDIO=y