binman: Support multithreading for building images

Some images may take a while to build, e.g. if they are large and use slow
compression. Support compiling sections in parallel to speed things up.

Signed-off-by: Simon Glass <sjg@chromium.org>
(fixed to use a separate test file to fix flakiness)

tools/binman/state.py

@@ -7,6 +7,7 @@
 
 import hashlib
 import re
+import threading
 
 from dtoc import fdt
 import os
@@ -55,6 +56,9 @@ allow_entry_expansion = True
 # to the new ones, the compressed size increases, etc.
 allow_entry_contraction = False
 
+# Number of threads to use for binman (None means machine-dependent)
+num_threads = None
+
 def GetFdtForEtype(etype):
     """Get the Fdt object for a particular device-tree entry
 
@@ -420,3 +424,22 @@ def AllowEntryContraction():
             raised
     """
     return allow_entry_contraction
+
+def SetThreads(threads):
+    """Set the number of threads to use when building sections
+
+    Args:
+        threads: Number of threads to use (None for default, 0 for
+            single-threaded)
+    """
+    global num_threads
+
+    num_threads = threads
+
+def GetThreads():
+    """Get the number of threads to use when building sections
+
+    Returns:
+        Number of threads to use (None for default, 0 for single-threaded)
+    """
+    return num_threads