gpu: nvgpu: add nvhost abstraction files

Add new abstraction file common/linux/nvhost.c for all
nvhost APIs and operations and export them from
header <nvgpu/nvhost.h>

This file will be compiled only if config
CONFIG_TEGRA_GK20A_NVHOST is set

Define struct nvgpu_nvhost_dev in a separate private
header nvhost_priv.h

Jira NVGPU-29

Change-Id: I17e1f7836d4854feadff0c339bc093e78ba7f3eb
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/1489725
Reviewed-by: svccoveritychecker <svccoveritychecker@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>

drivers/gpu/nvgpu/common/linux/nvhost_priv.h

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2017, NVIDIA CORPORATION.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __NVGPU_NVHOST_PRIV_H__
+#define __NVGPU_NVHOST_PRIV_H__
+
+struct nvgpu_nvhost_dev {
+	struct platform_device *host1x_pdev;
+};
+
+#endif /* __NVGPU_NVHOST_PRIV_H__ */