Add a reset driver framework/uclass

A reset controller is a hardware module that controls reset signals that
affect other hardware modules or chips.

This patch defines a standard API that connects reset clients (i.e. the
drivers for devices affected by reset signals) to drivers for reset
controllers/providers. Initially, DT is the only supported method for
connecting the two.

The DT binding specification (reset.txt) was taken from Linux kernel
v4.5's Documentation/devicetree/bindings/reset/reset.txt.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/Kconfig b/drivers/Kconfig
index f2a137a..f6003a0 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -56,6 +56,8 @@
 
 source "drivers/remoteproc/Kconfig"
 
+source "drivers/reset/Kconfig"
+
 source "drivers/rtc/Kconfig"
 
 source "drivers/serial/Kconfig"