reset: implement a reset test

This adds a sandbox reset implementation (provider), a test client
device, instantiates them both from Sandbox's DT, and adds a DM test
that excercises everything.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/reset/Kconfig b/drivers/reset/Kconfig
index 5c449a9..0fe8cc3 100644
--- a/drivers/reset/Kconfig
+++ b/drivers/reset/Kconfig
@@ -12,4 +12,12 @@
 	  although driving such reset isgnals using GPIOs may be more
 	  appropriate in this case.
 
+config SANDBOX_RESET
+	bool "Enable the sandbox reset test driver"
+	depends on DM_MAILBOX && SANDBOX
+	help
+	  Enable support for a test reset controller implementation, which
+	  simply accepts requests to reset various HW modules without actually
+	  doing anything beyond a little error checking.
+
 endmenu