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/M5253DEMO_defconfig b/configs/M5253DEMO_defconfig
index 3ed703a..79382eb 100644
--- a/configs/M5253DEMO_defconfig
+++ b/configs/M5253DEMO_defconfig
@@ -39,6 +39,7 @@
 CONFIG_SYS_I2C_SLAVE=0x7F
 CONFIG_SYS_I2C_SPEED=80000
 CONFIG_MTD_NOR_FLASH=y
+CONFIG_SYS_MAX_FLASH_SECT=2048
 CONFIG_USE_SYS_MAX_FLASH_BANKS=y
 CONFIG_DRIVER_DM9000=y
 CONFIG_MCFUART=y