Add support for media topology on Raspberry Pi 5

HDMI input over CSI2 on RPi5 requires quite a bit more setup, because
/dev/video0 (or other /dev/video*) isn't automatically routed to the
video source. This needs finding relevant source media entity, and then
a route to requested video device (usually /dev/video0). Setting video
format gets more complicated too, because it needs to be set on all
involved nodes (aka "pads").

V4L2_EVENT_SOURCE_CHANGE is delivered on a different FD than reading
stream from, so both needs to be select()ed in this case.

From the user perspective, this adds two new options: --media-device and
--media-entity-name. When provided, ustreamer will find requested entity
and route it to the device given in --device option.

src/libs/capture.h

@@ -51,8 +51,15 @@ typedef struct {
 	atomic_int			refs;
 } us_capture_hwbuf_s;
 
+typedef struct {
+	int fd;
+	uint pad;
+} us_media_pad_s;
+
 typedef struct {
 	int					fd;
+	int					dv_timings_fd;
+	us_media_pad_s				media_pads[3]; // for VIDIOC_SUBDEV_S_FMT
 	uint				width;
 	uint				height;
 	uint				format;
@@ -76,7 +83,7 @@ typedef enum {
 	CTL_MODE_DEFAULT,
 } us_control_mode_e;
 
-typedef struct {
+typedef struct _FD{
 	us_control_mode_e	mode;
 	int					value;
 } us_control_s;
@@ -103,6 +110,8 @@ typedef struct {
 	uint				width;
 	uint				height;
 	uint				format;
+	char				*media_path;
+	char				*media_entity_name;
 
 	bool				format_swap_rgb;
 	uint				jpeg_quality;