Disable VNDK and LLNDK renderscript libraries for riscv64

Renderscript does not support riscv64, disable the libraries that
are in the VNDK and LLNDK for riscv64 so that they don't break the
`m droid` build.

Test: lunch aosp_riscv64-userdebug && m droid
Change-Id: I8d9ff186b4946ce49169500f28f5d1f343f61255
diff --git a/Android.bp b/Android.bp
index cbc59cb..4189f30 100644
--- a/Android.bp
+++ b/Android.bp
@@ -53,6 +53,11 @@
     sanitize: {
         hwaddress: false, // code size b/112437884
     },
+    arch: {
+        riscv64: {
+            enabled: false,
+        },
+    },
 }
 
 // This module defines all of the defaults used to compiled llvm, except for