[Flag] Extend enable-experimental-kernel-vm-support flag

We will need this flag until we have completed the uprev of SKL-Y and
SKL-U Chrome OS systems to their new kernels.  It's unclear exactly when
this will be done, but my best guess right now is around M92.

BUG=b:144308685

Change-Id: I45b7b86641628184645912d4fdf3d616b6fd2c3c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2506301
Commit-Queue: Ross Zwisler <zwisler@google.com>
Auto-Submit: Ross Zwisler <zwisler@google.com>
Reviewed-by: David Munro <davidmunro@google.com>
Reviewed-by: Nic Hollingum <hollingum@google.com>
Reviewed-by: Nicholas Verne <nverne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822220}

chrome/browser/flag-metadata.json

@@ -1533,7 +1533,7 @@
   {
     "name": "enable-experimental-kernel-vm-support",
     "owners": [ "zwisler" ],
-    "expiry_milestone": 87
+    "expiry_milestone": 95
   },
   {
     "name": "enable-experimental-productivity-features",