ARM: dts: meson: add support for the Meson8m2 SoC

This adds a meson8m2.dtsi which simply inherits meson8.dtsi as both SoCs
share most peripherals.
The known differences are:
- Meson8m2's hardware video decoder additionally supports H.265 decoding
- Meson8m2 has the same Gigabit MAC as Meson8b (instead of the 10/100M
  MAC that Meson8 uses)
- Meson8m2 uses the same watchdog register layout/bits as Meson8b (using
  the Meson8 watchdog compatible leads to an infinite hang when
  rebooting the machine)
- Meson8m2 uses the same SAR ADC register layout/bits as Meson8b.
  However, it uses the temperature sensor calibration formula (and
  registers) Meson8b which differ from Meson8. This however is currently
  not supported by the meson-saradc driver yet.
- the pin controller is mostly compatible with Meson8, Meson8m2 has
  an additional function on eight pins and removes the "VGA" function.
  So there's a total of 10 pins which are slightly changed, which is why
  there's a separate compatible for the pin controller
- a separate compatible for the clock controller is used because at
  least the Mali clock tree (not supported yet) is the same as on GXBB
  while Meson8 and Meson8b have a reduced/older version of the Mali
  clock tree.
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

arch/arm/boot/dts/meson8m2.dtsi

+// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+/*
+ * Copyright (c) 2017 Martin Blumenstingl <martin.blumenstingl@googlemail.com>.
+ */
+
+#include "meson8.dtsi"
+
+/ {
+	model = "Amlogic Meson8m2 SoC";
+	compatible = "amlogic,meson8m2";
+}; /* end of / */
+
+&clkc {
+	compatible = "amlogic,meson8m2-clkc", "amlogic,meson8-clkc";
+};
+
+&ethmac {
+	compatible = "amlogic,meson8m2-dwmac", "snps,dwmac";
+	reg = <0xc9410000 0x10000
+		0xc1108140 0x8>;
+	clocks = <&clkc CLKID_ETH>,
+		 <&clkc CLKID_MPLL2>,
+		 <&clkc CLKID_MPLL2>;
+	clock-names = "stmmaceth", "clkin0", "clkin1";
+	resets = <&reset RESET_ETHERNET>;
+	reset-names = "stmmaceth";
+};
+
+&pinctrl_aobus {
+	compatible = "amlogic,meson8m2-aobus-pinctrl",
+		     "amlogic,meson8-aobus-pinctrl";
+};
+
+&pinctrl_cbus {
+	compatible = "amlogic,meson8m2-cbus-pinctrl",
+		     "amlogic,meson8-cbus-pinctrl";
+
+	eth_rgmii_pins: ethernet {
+		mux {
+			groups = "eth_tx_clk_50m", "eth_tx_en",
+				 "eth_txd3", "eth_txd2",
+				 "eth_txd1", "eth_txd0",
+				 "eth_rx_clk_in", "eth_rx_dv",
+				 "eth_rxd3", "eth_rxd2",
+				 "eth_rxd1", "eth_rxd0",
+				 "eth_mdio", "eth_mdc";
+			function = "ethernet";
+		};
+	};
+};
+
+&wdt {
+	compatible = "amlogic,meson8m2-wdt", "amlogic,meson8b-wdt";
+};