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/M5282EVB_defconfig b/configs/M5282EVB_defconfig
index aeb7738..751d805 100644
--- a/configs/M5282EVB_defconfig
+++ b/configs/M5282EVB_defconfig
@@ -34,6 +34,7 @@
 CONFIG_SYS_FLASH_PROTECTION=y
 CONFIG_SYS_FLASH_CFI=y
 CONFIG_SYS_FLASH_CHECKSUM=y
+CONFIG_SYS_MAX_FLASH_SECT=137
 CONFIG_DM_ETH=y
 CONFIG_MCFFEC=y
 CONFIG_MII=y