Add host_supported, min_sdk_version and apex_available configs to Android.bp for FP16.

This would solve build erros such as
"missing variant:os:linux_glibc,arch:x86_64" when adding
fp16_headers to external/tensorflow repo.

Bug: 196532440
Test: mma
Change-Id: Ia8ac144df6a18f17cc9c181ed8618a5d365abaa6
diff --git a/Android.bp b/Android.bp
index 3aaa01b..32b84f8 100644
--- a/Android.bp
+++ b/Android.bp
@@ -32,8 +32,16 @@
 cc_library_headers {
     name: "fp16_headers",
     export_include_dirs: ["include"],
+    host_supported: true,
     vendor_available: true,
     sdk_version: "current",
+    min_sdk_version: "30",
+    apex_available: [
+        "//apex_available:platform",
+        "com.android.neuralnetworks",
+        "test_com.android.neuralnetworks",
+        "com.android.extservices",
+    ],
 }
 
 cc_defaults {