Mark libF77blas as vendor_available

This is required by libblas, which is a vndk-sp library. Since this is a
static library, vendor_available: true is enough.

Bug: 64425518
Test: BOARD_VNDK_VERSION=current m -j libblas.vendor

Change-Id: I496a1f150719c15ac1c50508ebf9a097c5630347
diff --git a/blas/Android.bp b/blas/Android.bp
index 16d2f44..45a5178 100644
--- a/blas/Android.bp
+++ b/blas/Android.bp
@@ -47,6 +47,7 @@
 
 cc_library_static {
     name: "libF77blas",
+    vendor_available: true,
     defaults: ["eigen-defaults"],
     host_supported: true,
 }