vmbase: Move rand.rs out of pvmfw

The module isn't pvmfw-specific and could be re-used by other
vmbase-based code so move it. This will allow better future integration
with the TRNG already performed in vmbase/entry.S and with the C
interface exported by vmbase/src/bionic.rs.

Test: TH
Change-Id: I842425264c87cfe97618aceda371b410d7af6046
diff --git a/vmbase/src/lib.rs b/vmbase/src/lib.rs
index 54f3384..7fc7b20 100644
--- a/vmbase/src/lib.rs
+++ b/vmbase/src/lib.rs
@@ -23,11 +23,13 @@
 pub mod console;
 mod entry;
 pub mod fdt;
+mod hvc;
 pub mod layout;
 mod linker;
 pub mod logger;
 pub mod memory;
 pub mod power;
+pub mod rand;
 pub mod uart;
 pub mod util;
 pub mod virtio;