Boot: Extend flash layout for multiple images

This patch introduces the BOOT_IMAGE_NUMBER macro and current_image
variable to support multiple updatable images and the associated
extended flash layout.

The FLASH_AREA_IMAGE_* object-like macros are replaced with
function-like ones and therefore some functions have been updated,
because the labels of a switch statement and the initialization
values of objects with static storage duration have to be constant
expressions.

Change-Id: Ib7b26ec3c94233e52db4f97825ddb6a3e55bb1d3
Signed-off-by: David Vincze <david.vincze@arm.com>
diff --git a/boot/zephyr/include/sysflash/sysflash.h b/boot/zephyr/include/sysflash/sysflash.h
index 2492244..d4617bb 100644
--- a/boot/zephyr/include/sysflash/sysflash.h
+++ b/boot/zephyr/include/sysflash/sysflash.h
@@ -4,9 +4,32 @@
 #define __SYSFLASH_H__
 
 #include <generated_dts_board.h>
+#include <mcuboot_config/mcuboot_config.h>
 
+extern uint8_t current_image;
+
+#if (MCUBOOT_IMAGE_NUMBER == 1)
 #define FLASH_AREA_IMAGE_PRIMARY    DT_FLASH_AREA_IMAGE_0_ID
 #define FLASH_AREA_IMAGE_SECONDARY  DT_FLASH_AREA_IMAGE_1_ID
+#elif (MCUBOOT_IMAGE_NUMBER == 2)
+/* MCUBoot currently supports only up to 2 updateable firmware images.
+ * If the number of the current image is greater than MCUBOOT_IMAGE_NUMBER - 1
+ * then a dummy value will be assigned to the flash area macros.
+ */
+#define FLASH_AREA_IMAGE_PRIMARY    ((current_image == 0) ?         \
+                                         DT_FLASH_AREA_IMAGE_0_ID : \
+                                     (current_image == 1) ?         \
+                                         DT_FLASH_AREA_IMAGE_2_ID : \
+                                         255 )
+#define FLASH_AREA_IMAGE_SECONDARY  ((current_image == 0) ?         \
+                                         DT_FLASH_AREA_IMAGE_1_ID : \
+                                     (current_image == 1) ?         \
+                                         DT_FLASH_AREA_IMAGE_3_ID : \
+                                         255 )
+#else
+#error "Image slot and flash area mapping is not defined"
+#endif
+
 #define FLASH_AREA_IMAGE_SCRATCH    DT_FLASH_AREA_IMAGE_SCRATCH_ID
 
 #endif /* __SYSFLASH_H__ */