config/output: support DRM_FORMAT_ARGB8888

Some display output hardware [1] doesn't support any of the current
formats, but works with ARGB8888. Fall back to it if available.

[1] 196145c606/drivers/gpu/drm/xlnx/zynqmp_disp.c (L313)

Signed-off-by: Steffen Dirkwinkel <s.dirkwinkel@beckhoff.com>

sway/config/output.c

@@ -783,6 +783,7 @@ static bool search_render_format(struct search_context *ctx, size_t output_idx)
 		DRM_FORMAT_XRGB2101010,
 		DRM_FORMAT_XBGR2101010,
 		DRM_FORMAT_XRGB8888,
+		DRM_FORMAT_ARGB8888,
 		DRM_FORMAT_INVALID,
 	};
 	if (render_format_is_bgr(wlr_output->render_format)) {