Implement FAKE_CAMERA_SENSOR to allow fake image sensor used

Example, make `arducam_64mp` to behave as `imx519` as `imx519`
does have auto exposure control:

```
FAKE_CAMERA_SENSOR=arducam_64mp=imx519
```

device/libcamera/fake_camera.c

@@ -0,0 +1,65 @@
+#include <string.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <termios.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <sys/syscall.h>
+
+#include <linux/media.h>
+
+#include "opts/log.h"
+
+// This is special code to force `libcamera` to think that given sensor is different
+// ex.: fake `arducam_64mp` to be run as `imx519`
+
+void fake_camera_sensor(struct media_v2_topology *topology)
+{
+  struct media_v2_entity *ents = (struct media_v2_entity *)topology->ptr_entities;
+  if (!ents) {
+    return;
+  }
+
+  const char *fake_camera = getenv("FAKE_CAMERA_SENSOR");
+  if (!fake_camera) {
+    return;
+  }
+
+  char source[256];
+  sprintf(source, fake_camera);
+
+  char *target = strstr(source, "=");
+  if (!target) {
+    return;
+  }
+
+  *target++ = ' ';
+
+  for (int i = 0; i < topology->num_entities; i++) {
+    if (strncmp(ents[i].name, source, target-source) != 0) {
+      continue;
+    }
+
+    char name[sizeof(ents[i].name)];
+    strcpy(name, target);
+    strcat(name, " ");
+    strcat(name, ents[i].name + (target-source));
+    LOG_INFO(NULL, "Rewrote entity (%d): %s => %s", i, ents[i].name, name);
+    strcpy(ents[i].name, name);
+  }
+}
+
+int ioctl (int fd, unsigned long int req, ...)
+{
+  void *arg;
+  va_list ap;
+  va_start(ap, req);
+  arg = va_arg(ap, void *);
+  va_end(ap);
+  int ret = syscall(SYS_ioctl, fd, req, arg);
+  if (!ret && req == MEDIA_IOC_G_TOPOLOGY) {
+    fake_camera_sensor(arg);
+  }
+
+  return ret;
+}