reset: Add renesas,rst DT bindings

Add DT bindings for the Renesas R-Car Reset Controller (R-Car Gen1
RESET/WDT and R-Car Gen2/Gen3 and RZ/G RST).

As the features provided by the hardware module differ a lot across the
various SoC families and members, only SoC-specific compatible values
are defined.

For now we use the RST only for providing access to the state of the
mode pins, which is needed by the clock driver.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Magnus Damm <damm+renesas@opensource.se>
Acked-by: Dirk Behme <dirk.behme@de.bosch.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/reset/renesas,rst.txt

+DT bindings for the Renesas R-Car and RZ/G Reset Controllers
+
+The R-Car and RZ/G Reset Controllers provide reset control, and implement the
+following functions:
+  - Latching of the levels on mode pins when PRESET# is negated,
+  - Mode monitoring register,
+  - Reset control of peripheral devices (on R-Car Gen1),
+  - Watchdog timer (on R-Car Gen1),
+  - Register-based reset control and boot address registers for the various CPU
+    cores (on R-Car Gen2 and Gen3, and on RZ/G).
+
+
+Required properties:
+  - compatible: Should be
+		  - "renesas,<soctype>-reset-wdt" for R-Car Gen1,
+		  - "renesas,<soctype>-rst" for R-Car Gen2 and Gen3, and RZ/G
+		Examples with soctypes are:
+		  - "renesas,r8a7743-rst" (RZ/G1M)
+		  - "renesas,r8a7745-rst" (RZ/G1E)
+		  - "renesas,r8a7778-reset-wdt" (R-Car M1A)
+		  - "renesas,r8a7779-reset-wdt" (R-Car H1)
+		  - "renesas,r8a7790-rst" (R-Car H2)
+		  - "renesas,r8a7791-rst" (R-Car M2-W)
+		  - "renesas,r8a7792-rst" (R-Car V2H
+		  - "renesas,r8a7793-rst" (R-Car M2-N)
+		  - "renesas,r8a7794-rst" (R-Car E2)
+		  - "renesas,r8a7795-rst" (R-Car H3)
+		  - "renesas,r8a7796-rst" (R-Car M3-W)
+  - reg: Address start and address range for the device.
+
+
+Example:
+
+	rst: reset-controller@e6160000 {
+		compatible = "renesas,r8a7795-rst";
+		reg = <0 0xe6160000 0 0x0200>;
+	};