board: asus: transformer: add ASUS Transformer T30 family support

The ASUS Transformer T30 family are 2-in-1 detachable tablets
and AiO developed by ASUS that run the Android operating system
(TF600T runs Windows RT and P1801-T runs Android and Windows).
The T30 Transformers feature a 10.1-inch display (apart P1801-T),
an Nvidia Tegra 3 quad-core chip, 1/2 GB of RAM, and 16/32 GB of
storage. Transformers board derives from Nvidia Cardhu development
board.

This patch brings support for 7 known Transformer devices:
- ASUS Transformer Prime TF201
- ASUS Transformer Pad TF300T/TF300TG/TF300TL
- ASUS VivoTab RT TF600T (Windows RT based)
- ASUS Transformer Infinity TF700T
- ASUS Portable AiO P1801-T

Tested-by: Andreas Westman Dorcsak <hedmoo@yahoo.com> # all devices
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
diff --git a/arch/arm/dts/tegra30-asus-tf300t.dts b/arch/arm/dts/tegra30-asus-tf300t.dts
new file mode 100644
index 0000000..db08488
--- /dev/null
+++ b/arch/arm/dts/tegra30-asus-tf300t.dts
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: GPL-2.0
+/dts-v1/;
+
+#include "tegra30-asus-transformer.dtsi"
+
+/ {
+	model = "ASUS Transformer Pad TF300T";
+	compatible = "asus,tf300t", "nvidia,tegra30";
+
+	gpio@6000d000 {
+		volume-buttons-hog {
+			gpio-hog;
+			gpios = <TEGRA_GPIO(R, 0) GPIO_ACTIVE_HIGH>,
+				<TEGRA_GPIO(K, 7) GPIO_ACTIVE_HIGH>;
+			output-low;
+		};
+	};
+};