Hard-code two build properties in build.prop

These two properties are necessary for the default keymint HAL.

Bug: 189164487
Test: boot and getprop
Change-Id: I9b387da8e5b6df86eaa0ab76ddadfcdeab0d1b09
diff --git a/microdroid/build.prop b/microdroid/build.prop
index 52d073f..b7f3510 100644
--- a/microdroid/build.prop
+++ b/microdroid/build.prop
@@ -2,3 +2,7 @@
 ro.apex.updatable=true
 ro.debuggable=1
 ro.adb.secure=0
+
+# TODO(b/189164487): support build related properties
+ro.build.version.release=11
+ro.build.version.security_patch=2021-07-05