Add a capability query for image number

In addition to the binary capability flags, add a query function that
returns the number of images MCUboot has been configured to support.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/boot/bootutil/include/bootutil/caps.h b/boot/bootutil/include/bootutil/caps.h
index dc4ba4a..2b1f754 100644
--- a/boot/bootutil/include/bootutil/caps.h
+++ b/boot/bootutil/include/bootutil/caps.h
@@ -41,6 +41,12 @@
 #define BOOTUTIL_CAP_ENC_KW                 (1<<6)
 #define BOOTUTIL_CAP_VALIDATE_PRIMARY_SLOT  (1<<7)
 
+/*
+ * Query the number of images this bootloader is configured for.  This
+ * is also primarily used for testing.
+ */
+uint32_t bootutil_get_num_images(void);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/boot/bootutil/src/caps.c b/boot/bootutil/src/caps.c
index 83b4dfa..b449a6b 100644
--- a/boot/bootutil/src/caps.c
+++ b/boot/bootutil/src/caps.c
@@ -47,3 +47,12 @@
 
     return res;
 }
+
+uint32_t bootutil_get_num_images(void)
+{
+#if defined(MCUBOOT_IMAGE_NUMBER)
+    return MCUBOOT_IMAGE_NUMBER;
+#else
+    return 1;
+#endif
+}