dtoc: Support multiple compatible strings in a node

Sometimes a node will have multiple compatible strings. Drivers may use
one or the other so the best approach seems to be to #define them to be
equivalent.

Update dtoc to support this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/doc/driver-model/of-plat.txt b/doc/driver-model/of-plat.txt
index 0063bfe..3ed8c75 100644
--- a/doc/driver-model/of-plat.txt
+++ b/doc/driver-model/of-plat.txt
@@ -156,6 +156,11 @@
 platform data in the driver. The ofdata_to_platdata() method should
 therefore do nothing in such a driver.
 
+Where a node has multiple compatible strings, a #define is used to make them
+equivalent, e.g.:
+
+#define dtd_rockchip_rk3299_dw_mshc dtd_rockchip_rk3288_dw_mshc
+
 
 Converting of-platdata to a useful form
 ---------------------------------------