Fix tests on aosp_cf_x86_64_only_phone

Our nested virtualization check failed on this target. Move to a
prefix check to support this device and any other ones that appear.

Also extract the code to do the check to a library, rather than
changing in two places.

Bug: 236922543
Test: Presubmit
Change-Id: Id1d424f5f107e2098d89ca2ea8089ba956f212ca
diff --git a/virtualizationservice/Android.bp b/virtualizationservice/Android.bp
index 791da24..0c9496a 100644
--- a/virtualizationservice/Android.bp
+++ b/virtualizationservice/Android.bp
@@ -35,6 +35,7 @@
         "liblog_rust",
         "libmicrodroid_metadata",
         "libmicrodroid_payload_config",
+        "libnested_virt",
         "libnix",
         "libonce_cell",
         "libregex",