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/M5235EVB_defconfig b/configs/M5235EVB_defconfig
index a14bf42..7f7d92b 100644
--- a/configs/M5235EVB_defconfig
+++ b/configs/M5235EVB_defconfig
@@ -45,6 +45,7 @@
 CONFIG_SYS_FLASH_CFI_WIDTH_16BIT=y
 CONFIG_SYS_FLASH_PROTECTION=y
 CONFIG_SYS_FLASH_CFI=y
+CONFIG_SYS_MAX_FLASH_SECT=137
 CONFIG_DM_ETH=y
 CONFIG_MCFFEC=y
 CONFIG_MII=y