Copy kernel prebuilt from GKI

In preparation for switching from GKI to microdroid_kernel, copy the
current GKI to the local directory. The following CLs will update this
GKI with the microdroid_kernel.

Bug: 231117670
Test: N/A

Change-Id: I98da8c3bc3295a4c08729a38a2714bd15c6cf3b4
diff --git a/microdroid/kernel/arm64/prebuilt-info.txt b/microdroid/kernel/arm64/prebuilt-info.txt
new file mode 100644
index 0000000..dc32e4b
--- /dev/null
+++ b/microdroid/kernel/arm64/prebuilt-info.txt
@@ -0,0 +1,3 @@
+{
+    "kernel-build-id": 8704934
+}