dtc: Rework handling of boot_cpuid_phys

Currently, dtc will put the nonsense value 0xfeedbeef into the
boot_cpuid_phys field of an output blob, unless explicitly given
another value with the -b command line option.  As well as being a
totally unuseful default value, this also means that dtc won't
properly preserve the boot_cpuid_phys field in -I dtb -O dtb mode.

This patch reworks things to improve the boot_cpuid handling.  The new
semantics are that the output's boot_cpuid_phys value is:
	the value given on the command line if -b is used
otherwise
	the value from the input, if in -I dtb mode
otherwise
	0

Implementation-wise we do the following:
	- boot_cpuid_phys is added to struct boot_info, so that
structure now contains all of the blob's semantic information.
	- dt_to_blob() and dt_to_asm() output the cpuid given in
boot_info
	- dt_from_blob() fills in boot_info based on the input blob
	- The other dt_from_*() functions just record 0, but we can
change this easily if e.g. we invent a way of specifying the boot cpu
in the source format.
	- main() overrides the cpuid in the boot_info between input
and output if -b is given

We add some testcases to check this new behaviour.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

fstree.c

@@ -87,6 +87,6 @@ struct boot_info *dt_from_fs(const char *dirname)
 	tree = read_fstree(dirname);
 	tree = name_node(tree, "", NULL);
 
-	return build_boot_info(NULL, tree);
+	return build_boot_info(NULL, tree, 0);
 }