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/amcore_defconfig b/configs/amcore_defconfig
index ad549c0..71ee979 100644
--- a/configs/amcore_defconfig
+++ b/configs/amcore_defconfig
@@ -35,4 +35,5 @@
 CONFIG_FLASH_CFI_DRIVER=y
 CONFIG_SYS_FLASH_USE_BUFFER_WRITE=y
 CONFIG_SYS_FLASH_CFI=y
+CONFIG_SYS_MAX_FLASH_SECT=1024
 CONFIG_MCFUART=y