radv: Add KHR_display extension to radv [v5]

radv: Add KHR_display extension to radv [v5]

This adds support for the KHR_display extension to the radv Vulkan
driver. The driver now attempts to open the master DRM node when the
KHR_display extension is requested so that the common winsys code can
perform the necessary operations.

v2:
	* Simplify addition of VK_USE_PLATFORM_DISPLAY_KHR to
          vulkan_wsi_args

	Suggested-by: Eric Engestrom <eric.engestrom@imgtec.com>
v3:
	Adapt to new wsi_device_init API (added display_fd)

v4:
	Adopt Jason Ekstrand's coding conventions

	Declare variables at first use, eliminate extra whitespace
	between types and names. Wrap lines to 80 columns.

	Suggested-by: Jason Ekstrand <jason.ekstrand@intel.com>
v5:
	Add vkCreateDisplayModeKHR. This doesn't actually create
	new modes, it only looks to see if the requested parameters
	matches an existing mode and returns that.

    	Suggested-by: Jason Ekstrand <jason.ekstrand@intel.com>
Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>