dtoc: Convert _drivers to a dict

At present this member holds a simple list of driver names. Update it to
be a dict of DriverInfo, with the name being the key. This will allow more
information to be added about each driver, in future patches.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/dtoc/test_dtoc.py b/tools/dtoc/test_dtoc.py
index 49ab75b..c76942c 100755
--- a/tools/dtoc/test_dtoc.py
+++ b/tools/dtoc/test_dtoc.py
@@ -906,3 +906,13 @@
         with test_util.capture_sys_output() as (stdout, stderr):
             dtb_platdata.run_steps(['struct'], dtb_file, False, output, True,
                                [driver_fn])
+
+    def testDriver(self):
+        """Test the Driver class"""
+        drv1 = dtb_platdata.Driver('fred')
+        drv2 = dtb_platdata.Driver('mary')
+        drv3 = dtb_platdata.Driver('fred')
+        self.assertEqual("Driver(name='fred')", str(drv1))
+        self.assertEqual(drv1, drv3)
+        self.assertNotEqual(drv1, drv2)
+        self.assertNotEqual(drv2, drv3)