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/M5272C3_defconfig b/configs/M5272C3_defconfig
index e3f736b..7dc87a2 100644
--- a/configs/M5272C3_defconfig
+++ b/configs/M5272C3_defconfig
@@ -57,6 +57,7 @@
 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