vmbase: Re-expose fdtpci as vmbase::fdt::pci

All users of the crate are VM guest kernels, which are also using vmbase
so streamline the dependency graph by (for now) removing fdtpci from
their explicit dependencies and re-exposing its functionality as a
module of the vmbase crate.

Note: No functional change intended.

Test: TH
Change-Id: I384dab5267813936237626ee7286376ca7aa6ebd
diff --git a/libs/libvmbase/src/fdt.rs b/libs/libvmbase/src/fdt.rs
index 4101f7e..8618acd 100644
--- a/libs/libvmbase/src/fdt.rs
+++ b/libs/libvmbase/src/fdt.rs
@@ -52,3 +52,8 @@
         self.addr.map(|addr| addr..addr + self.size)
     }
 }
+
+/// Library for working with (VirtIO) PCI devices discovered from a device tree.
+pub mod pci {
+    pub use fdtpci::*;
+}