vmbase: Clean up TRNG_RND64 result byte order

Clarify the code extracting the entropy from the 3-register result of
RND64 calls and address what was probably a bug on big-endian where
using .to_ne_bytes() with (n_bytes % size_of::<u64>()) != 0 would have
resulted in the wrong bytes being used to populate the chunk.

In turn, use the newly introduced slice to simplify fill_with_entropy().

Test: atest DebugPolicyHostTests#testNoAdbInDebugPolicy_withDebugLevelNone_boots
Test: atest rialto_test vmbase_example.integration_test
Change-Id: Iefba4d977352abe5d3001ef44721f368f2ceeee6
diff --git a/vmbase/Android.bp b/vmbase/Android.bp
index 46f4937..71b9e76 100644
--- a/vmbase/Android.bp
+++ b/vmbase/Android.bp
@@ -84,6 +84,7 @@
         "libspin_nostd",
         "libtinyvec_nostd",
         "libvirtio_drivers",
+        "libzerocopy_nostd",
         "libzeroize_nostd",
     ],
     whole_static_libs: [