cros_setup_toolchains: support "all" with --show-board-cfg

We have some tools that want to query all the available tuples,
so add support for doing that.

BUG=None
TEST=`cros_setup_toolchains --show-board-cfg=all` shows all tuples from all boards

Change-Id: I4d24f3a8c9bf3d16ade18f25c02a28aaeb50825f
Reviewed-on: https://gerrit.chromium.org/gerrit/24332
Reviewed-by: Zdenek Behan <zbehan@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Ready: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cros_setup_toolchains.py b/scripts/cros_setup_toolchains.py
index 7c91b76..6381874 100644
--- a/scripts/cros_setup_toolchains.py
+++ b/scripts/cros_setup_toolchains.py
@@ -190,11 +190,7 @@
 
   returns the list of cross targets for the current tree
   """
-  cmd = [CROS_OVERLAY_LIST_CMD, '--all_boards']
-  overlays = cros_build_lib.RunCommand(cmd, print_cmd=False,
-                                       redirect_stdout=True).output.splitlines()
-
-  targets = GetTuplesForOverlays(overlays)
+  targets = GetToolchainsForBoard('all')
 
   # Remove the host target as that is not a cross-target. Replace with 'host'.
   targets.discard(GetHostTuple())
@@ -206,7 +202,11 @@
 
   returns the list of toolchain tuples for the given board
   """
-  cmd = [CROS_OVERLAY_LIST_CMD, '--board=' + board]
+  cmd = [CROS_OVERLAY_LIST_CMD]
+  if board == 'all':
+    cmd.append('--all_boards')
+  else:
+    cmd.append('--board=' + board)
   overlays = cros_build_lib.RunCommand(
       cmd, print_cmd=False, redirect_stdout=True).output.splitlines()