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/pvmfw/src/instance.rs b/pvmfw/src/instance.rs
index 56468b2..1035559 100644
--- a/pvmfw/src/instance.rs
+++ b/pvmfw/src/instance.rs
@@ -21,7 +21,6 @@
 use crate::gpt;
 use crate::gpt::Partition;
 use crate::gpt::Partitions;
-use crate::rand;
 use core::fmt;
 use core::mem::size_of;
 use diced_open_dice::DiceMode;
@@ -30,6 +29,7 @@
 use log::trace;
 use uuid::Uuid;
 use virtio_drivers::transport::{pci::bus::PciRoot, DeviceType, Transport};
+use vmbase::rand;
 use vmbase::util::ceiling_div;
 use vmbase::virtio::pci::{PciTransportIterator, VirtIOBlk};
 use zerocopy::AsBytes;