efi: Add an efi subcommand to show the loaded image

Sometimes it is useful to see the device-path of the app itself. Add a
new 'efi image' command for this.

Signed-off-by: Simon Glass <sjg@chromium.org>

doc/usage/cmd/efi.rst

@@ -12,6 +12,7 @@ Synopsis
 
 ::
 
+    efi image
     efi mem [all]
     efi tables
 
@@ -26,6 +27,16 @@ information. When running as an EFI payload, EFI boot services have been
 stopped, so it uses the information collected by the boot stub before that
 happened.
 
+efi image
+~~~~~~~~~
+
+This shows the loaded image path information for the currently running EFI
+application. The loaded image protocol provides access to the device path
+from which the image was loaded.
+
+The output shows the file path in EFI device path format, displayed as a
+human-readable Unicode string.
+
 efi mem
 ~~~~~~~
 
@@ -71,6 +82,9 @@ Example
 
 ::
 
+    => efi image
+    Loaded-image path: u-boot-app.efi
+
     => efi mem
     EFI table at 0, memory map 000000001ad38b60, size 1260, key a79, version 1, descr. size 0x30
      #  Type              Physical     Virtual        Size  Attributes