bootutil: Add debug logging for boot status write

Adds debug level logging which shows the offset of where a
sector swap status write is occurring at

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
diff --git a/boot/bootutil/src/loader.c b/boot/bootutil/src/loader.c
index 8bbabbb..9a771a0 100644
--- a/boot/bootutil/src/loader.c
+++ b/boot/bootutil/src/loader.c
@@ -470,6 +470,10 @@
     memset(buf, erased_val, BOOT_MAX_ALIGN);
     buf[0] = bs->state;
 
+    BOOT_LOG_DBG("writing swap status; fa_id=%d off=0x%lx (0x%lx)",
+                 flash_area_get_id(fap), (unsigned long)off,
+                 (unsigned long)flash_area_get_off(fap) + off);
+
     rc = flash_area_write(fap, off, buf, align);
     if (rc != 0) {
         rc = BOOT_EFLASH;