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/clk/clk_sandbox_test.c b/drivers/clk/clk_sandbox_test.c
index 4195466..628110d 100644
--- a/drivers/clk/clk_sandbox_test.c
+++ b/drivers/clk/clk_sandbox_test.c
@@ -7,6 +7,7 @@
 #include <dm.h>
 #include <clk.h>
 #include <asm/clk.h>
+#include <linux/err.h>
 
 struct sandbox_clk_test {
 	struct clk clks[SANDBOX_CLK_TEST_NON_DEVM_COUNT];