mtd: cfi: change CONFIG_SYS_MAX_FLASH_BANKS_DETECT as boolean

Prepare migration to Kconfig.

CONFIG_SYS_MAX_FLASH_BANKS_DETECT becomes boolean and
CONFIG_SYS_MAX_FLASH_BANKS define the MAX size, also used
for detection when CONFIG_SYS_MAX_FLASH_BANKS_DETECT=y
(CFI_MAX_FLASH_BANKS = CONFIG_SYS_MAX_FLASH_BANKS).

CONFIG_SYS_MAX_FLASH_BANKS become mandatory when
CONFIG_SYS_MAX_FLASH_BANKS_DETECT is activated.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/include/configs/boston.h b/include/configs/boston.h
index cd70e7b..7ac044e 100644
--- a/include/configs/boston.h
+++ b/include/configs/boston.h
@@ -40,7 +40,9 @@
 /*
  * Flash
  */
-#define CONFIG_SYS_MAX_FLASH_BANKS_DETECT	1
+
+#define CONFIG_SYS_MAX_FLASH_BANKS	1
+#define CONFIG_SYS_MAX_FLASH_BANKS_DETECT
 #define CONFIG_SYS_MAX_FLASH_SECT		1024
 
 /*