net/mlx5: add OS specific flow related utilities

net/mlx5: add OS specific flow related utilities

This patch introduces the first OS specific utility functions,
for use by flow engine in different OS implementation.

The first utility functions are:
bool mlx5_flow_os_item_supported(item)
bool mlx5_flow_os_action_supported(action)

They are implemented to check OS specific support for different
item types and action types.

New header file is added:
drivers/net/mlx5/linux/mlx5_flow_os.h

This file contains the utility functions mentioned above for Linux OS.
At this stage they are implemented as static inline, for efficiency,
and always return true.

Signed-off-by: Dekel Peled <dekelp@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>