rework BootParams struct for extensibility

* boot parameters and corresponding addresses are separate fields
  in the struct, instead of packed in a tuple
* sections and modules (for PVH boot) can be added one at a time
  and don't need to be of the same type

Signed-off-by: Alexandra Iordache <aghecen@amazon.com>

Author: Alexandra Iordache

coverage_config_aarch64.json

@@ -1,5 +1,5 @@
 {
-  "coverage_score": 77.2,
+  "coverage_score": 79.9,
   "exclude_path": "",
   "crate_features": ""
 }

coverage_config_x86_64.json

@@ -1,5 +1,5 @@
 {
-  "coverage_score": 77.8,
+  "coverage_score": 78.5,
   "exclude_path": "",
   "crate_features": ""
 }

src/configurator/aarch64/fdt.rs

@@ -59,7 +59,7 @@ impl BootConfigurator for FdtBootConfigurator {
     {
         // The VMM has filled an FDT and passed it as a `ByteValued` object.
         guest_memory
-            .write_slice(params.header.0.as_slice(), params.header.1)
+            .write_slice(params.header.as_slice(), params.header_start)
             .map_err(|_| Error::WriteFDTToMemory.into())
     }
 }