HDMI display test

EC-A1684XJD4 does not have a graphics card chip, and the HDMI output
part of the main control does not use the standard framebuffer driver.
When it is shipped from the factory, it is not displayed when it is
connected to HDMI.

If the user wants to test the HDMI display, he can connect to the HDMI
interface, and then execute the "test-hdmi" script:

   linaro@bm1684:~$ sudo -i
   root@bm1684:~# test-hdmi
   found (1024, 768) @ 60 fps
   entry[0] = (1024, 768) added
   found (1024, 768) @ 60 fps
   found (1024, 768) @ 60 fps
   found (1024, 768) @ 60 fps
   found (1024, 768) @ 60 fps
   found (1024, 768) @ 60 fps
   found (1024, 768) @ 60 fps
   found (1024, 768) @ 60 fps
   found (1920, 1080) detailed timing desc
   entry [1] = (1920, 1080) added
   found (1920, 1080) detailed timing desc
   found (1920, 1080) detailed timing desc
   found (1920, 1080) detailed timing desc