media: aspeed: add debugfs

To show video real-time information as below:

Capture:
  Signal              : Unlock
  Width               : 1920
  Height              : 1080
  FRC                 : 30

Performance:
  Frame#              : 0
  Frame Duration(ms)  :
    Now               : 0
    Min               : 0
    Max               : 0
  FPS                 : 0

[hverkuil: make aspeed_video_proc_open() static, fixes sparse warning]

Signed-off-by: Jammy Huang <jammy_huang@aspeedtech.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>