sw-update: provide usage info

with option -h or with invalid arguments a usage info is printed to the
console.

BugzID: 53654

Signed-off-by: Patrick Zysset <patrick.zysset@netmodule.com>

recipes-core/sw-update/sw-update/sw-update.sh

@@ -276,6 +276,12 @@ update_spl()
   log INFO "spl update succeed!"
 }
 
+usage()
+{
+  echo "Usage: $0 [ -l <linux-image>.tar.gz ] [ -u <u-boot>.img ] [ -s <spl>.img ] [ -h ]"
+  exit 2
+}
+
 ############################ Start of script ###################################
 
 if [ ! -b $PLATFORM_MAIN_STORAGE ]; then
@@ -295,7 +301,11 @@ while getopts ":l:u:s:h" opt; do
       update_spl $OPTARG
       ;;
     h)
-      echo "Invalid option: -$OPTARG" >&2
+      usage
+      ;;
+    ?)
+      log INFO "Invalid option: -$OPTARG"
+      usage
       ;;
   esac
 done