Revert "Remove references to android15-6.1 microdroid kernel"

This reverts commit befa999518814215f9b68f2bafbbb564401743b0.

Reason for revert: Likely culprit for b/352525023  - verifying through ABTD before revert submission. This is part of the standard investigation process, and does not mean your CL will be reverted.

Change-Id: I58a0eab8cb797fc7ccdf40840d146bba41e8a4f6
diff --git a/microdroid/kernel/android15-6.1/arm64/prebuilt-info.txt b/microdroid/kernel/android15-6.1/arm64/prebuilt-info.txt
new file mode 100644
index 0000000..edc832f
--- /dev/null
+++ b/microdroid/kernel/android15-6.1/arm64/prebuilt-info.txt
@@ -0,0 +1,3 @@
+{
+    "kernel-build-id": "11448237"
+}