net/mlx5: DR, Change SWS usage to debug fs seq_file interface

In current SWS debug dump mechanism we implement the seq_file interface,
but we only implement the 'show' callback to dump the whole steering DB
with a single call to this callback.

However, for large data size the seq_printf function will fail to
allocate a buffer with the adequate capacity to hold such data.

This patch solves this problem by utilizing the seq_file interface
mechanism in the following way:
 - when the user triggers a dump procedure, we will allocate a list of
   buffers that hold the whole data dump (in the start callback)
 - using the start, next, show and stop callbacks of the seq_file
   API we iterate through the list and dump the whole data
Signed-off-by: Hamdan Igbaria <hamdani@nvidia.com>
Reviewed-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>

drivers/net/ethernet/mellanox/mlx5/core/steering/dr_dbg.h

 /* SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB */
 /* Copyright (c) 2021, NVIDIA CORPORATION & AFFILIATES. All rights reserved. */
 
+#define MLX5DR_DEBUG_DUMP_BUFF_SIZE (64 * 1024 * 1024)
+#define MLX5DR_DEBUG_DUMP_BUFF_LENGTH 512
+
+enum {
+	MLX5DR_DEBUG_DUMP_STATE_FREE,
+	MLX5DR_DEBUG_DUMP_STATE_IN_PROGRESS,
+};
+
+struct mlx5dr_dbg_dump_buff {
+	char *buff;
+	u32 index;
+	struct list_head node;
+};
+
+struct mlx5dr_dbg_dump_data {
+	struct list_head buff_list;
+};
+
 struct mlx5dr_dbg_dump_info {
 	struct mutex dbg_mutex; /* protect dbg lists */
 	struct dentry *steering_debugfs;
 	struct dentry *fdb_debugfs;
+	struct mlx5dr_dbg_dump_data *dump_data;
+	atomic_t state;
 };
 
 void mlx5dr_dbg_init_dump(struct mlx5dr_domain *dmn);