Add fuchsia/update_images.py to v8/DEPS

According to this change in chromium's DEPS
https://chromium-review.googlesource.com/c/chromium/src/+/2446832

Bug: chromium:1137317
No-Try: true
No-Presubmit: true
Change-Id: I2b9e804f151834b58b77db1aca591e2eade91243
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2465826
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Auto-Submit: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70448}

DEPS

@@ -519,12 +519,21 @@ hooks = [
                '-o', 'build/util/LASTCHANGE'],
   },
   {
-    'name': 'fuchsia_sdk',
+    'name': 'Download Fuchsia SDK',
     'pattern': '.',
     'condition': 'checkout_fuchsia',
     'action': [
       'python',
       'build/fuchsia/update_sdk.py',
+    ],
+  },
+  {
+    'name': 'Download Fuchsia system images',
+    'pattern': '.',
+    'condition': 'checkout_fuchsia',
+    'action': [
+      'python',
+      'build/fuchsia/update_images.py',
       '--boot-images={checkout_fuchsia_boot_images}',
     ],
   },