Make vidioc_g_fmt_out not change the format

If vidioc_g_fmt_out was called after vidioc_s_fmt_out but before
vidioc_streamon, it would reset the format to default. This is incorrect
behaviour.

Moved the setting of initial format to device init instead.
Set correct output buffer type in vidioc_dqbuf

When userspace dequeues an output buffer from the driver, that buffer should
have type V4L2_BUF_TYPE_VIDEO_OUTPUT. Previously we were providing the type
from our internal buffer which is V4L2_BUF_TYPE_VIDEO_CAPTURE.
Merge remote-tracking branch 'remotes/pullrequest/fix_g_fmt' into experimental
Merge remote-tracking branch 'remotes/pullrequest/fix_buf_type' into experimental