arch: Add logging for FDT debugging on AArch64

To debug the FDT (Flattened Device Tree), we usually need to modify
source code to save the generted DTB data to disk, and use 'dtc' command
to decode the binary file into a text file to analyze.

It would be ideal if the FDT content can be seen in log.

This commit makes it real by:
- Introducing 'fdt' crate for parsing FDT.
- Printing the content of the FDT in tree view.

The parsing and printing only happen when Debug level logging enabled.

Signed-off-by: Michael Zhao <michael.zhao@arm.com>

arch/src/aarch64/mod.rs

@@ -18,6 +18,7 @@ use crate::DeviceType;
 use crate::GuestMemoryMmap;
 use crate::RegionType;
 use gic::GicDevice;
+use log::{log_enabled, Level};
 use std::collections::HashMap;
 use std::convert::TryInto;
 use std::ffi::CStr;
@@ -154,6 +155,10 @@ pub fn configure_system<T: DeviceInfoForFdt + Clone + Debug, S: ::std::hash::Bui
     )
     .map_err(|_| Error::SetupFdt)?;
 
+    if log_enabled!(Level::Debug) {
+        fdt::print_fdt(&fdt_final);
+    }
+
     fdt::write_fdt_to_memory(fdt_final, guest_mem).map_err(Error::WriteFdtToMemory)?;
 
     Ok(())