v4l2src: Add source-change / resolution-change support

This branch adds support for driver driven source changes along with DV_TIMING locking support. Effectively, drivers can emit SOURCE_CHANGE event, with the RESOLUTION_CHANGE flag in order to signal that something got changes at the input signal. In that situation, we need to reset (streamoff/on) as we may not get more data otherwise. While doing this, we now query for detected DV_TIMING (aka modes) and lock/set these. We also default to the link detected width/height/framerate.

As a bonus, v4l2src will now mimic decklinksrc when the signal is lost and recovered. A WARNING with RESSOURCE/READ will be emited when the signal is lost, and an INFO message again with RESSOURCE/READ for when it's recovered.

This has been tested with vivid test driver and an work in progress HDMI receiver driver.

Note to myself, probably just one of many typos:

- v4l2rc: Add DV_TIMINGS query and locking 
+ v4l2src: Add DV_TIMINGS query and locking 

added 38 commits

• a2de405c...1b1ad32b - 22 commits from branch gstreamer:master
• 69a1f7fc - v4l2bufferpool: use FLOW_LAST_BUFFER
• 2667a2a3 - v4l2object: Add event helpers
• cb00e9af - v4l2bufferpool: Handle resolution change event
• 9279e7f1 - v4l2src: Add source resolution change support
• 9a93c1ea - v4l2: Fix input/output index sign
• 80d7d815 - v4l2: Add helper to query input status
• ddb33fe1 - v4l2src: Add input signal status detection
• 6cb27d0d - v4l2: Subscribe source_change for the current input
• 8f6ed2fb - v4l2src: Stub preferred resolution support
• c3eab24a - v4l2src: Refactor to use PreferredCapsInfo structure
• 7086549e - v4l2object: Remove unused streaming member
• 3caa4f70 - v4l2src: Force renegotiation on resolution change
• a551ed24 - v4l2rc: Add DV_TIMINGS query and locking
• b8db9f50 - v4l2src: Calculate framerate from DV timings
• 2a0e6a47 - v4l2src: Move preferred resolution query before the probe
• 85040668 - v4l2bufferpool: Silence traces around unsupported source change

Compare with previous version

added 14 commits

• 6fdb6812 - v4l2bufferpool: Handle resolution change event
• eb9e8294 - v4l2src: Add source resolution change support
• daea11e7 - v4l2: Fix input/output index sign
• 458f4554 - v4l2: Add helper to query input status
• 897eee9a - v4l2src: Add input signal status detection
• 0b2da991 - v4l2: Subscribe source_change for the current input
• 806976a2 - v4l2src: Stub preferred resolution support
• 41083865 - v4l2src: Refactor to use PreferredCapsInfo structure
• 08307981 - v4l2object: Remove unused streaming member
• e0c415cc - v4l2src: Force renegotiation on resolution change
• c597889f - v4l2rc: Add DV_TIMINGS query and locking
• 362906c2 - v4l2src: Calculate framerate from DV timings
• 97649cb7 - v4l2src: Move preferred resolution query before the probe
• ba442c4a - v4l2bufferpool: Silence traces around unsupported source change

Compare with previous version

resolved all threads

assigned to @gstreamer-merge-bot

mentioned in commit ndufresne/gst-plugins-good@748fc7e8

mentioned in commit ndufresne/gst-plugins-good@f596dcdd

mentioned in commit ndufresne/gst-plugins-good@2b309ba0