reset: Add reset controller API

This adds a simple API for devices to request being reset
by separate reset controller hardware and implements the
reset signal device tree binding.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Pavel Machek <pavel@ucw.cz>

drivers/Makefile

diff --git a/drivers/Makefile b/drivers/Makefile
index dce39a9..1a64c4c 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -37,6 +37,9 @@
 # regulators early, since some subsystems rely on them to initialize
 obj-$(CONFIG_REGULATOR)		+= regulator/
 
+# reset controllers early, since gpu drivers might rely on them to initialize
+obj-$(CONFIG_RESET_CONTROLLER)	+= reset/
+
 # tty/ comes before char/ so that the VT console is the boot-time
 # default.
 obj-y				+= tty/