dm: core: Require users of devres to include the header

At present devres.h is included in all files that include dm.h but few
make use of it. Also this pulls in linux/compat which adds several more
headers. Drop the automatic inclusion and require files to include devres
themselves. This provides a good indication of which files use devres.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Anatolij Gustschin <agust@denx.de>
diff --git a/drivers/serial/serial_sifive.c b/drivers/serial/serial_sifive.c
index c142ccd..5a02f0c 100644
--- a/drivers/serial/serial_sifive.c
+++ b/drivers/serial/serial_sifive.c
@@ -13,6 +13,7 @@
 #include <asm/io.h>
 #include <linux/compiler.h>
 #include <serial.h>
+#include <linux/err.h>
 
 DECLARE_GLOBAL_DATA_PTR;