[intel-gfx] Displayport compliance testing

[Todd Previte <tprevite@gmail.com>]

The kernel side is responsible for the acknowledgement of the test requests and 
setup of the required parameters. It also handles the necessary AUX transactions 
for reading the EDID and DPCD as well as writing response codes or checksums as 
necessary. Performing these operations in userspace would add unnecessary delays 
and complicate the interface more than necessary. The userspace application then 
handles the large motions - frame buffer management, mode sets and link 
configuration. The following is an overview of the basic event handling for 
compliance testing inside the kernel:
        - The test device  signals the DUT with an HPD pulse. This can  be a 
          short or long pulse, depending on circumstances.
        - The interrupt generated by the HPD pulse invokes the test handler, 
          which reads the test device DPCD to determine what actions are necessary.
        - Once the test handler determines which test has been requested, it 
          invokes the kernel-side handler function and then signals the userspace 
          app. If no userspace app has been registered, the signal is ignored.
        - Test responses and status is written out / reported as necessary and 
          normal operation is resumed.

The userspace support application and additional documentation will be posted 
to the list for review soon.