timing: add edge-edge mode and delta calculation

Instead of only measuring the timing from any edge to any edge, provide
a mode to measure the times from falling->falling and rising->rising
edges. This works better to monitor timing of an IRQ pin for instance,
that drives one direction under hardware, and is only cleared by
software reading a value.

Include time delta measurements as an optional annotation to help track
jitter in measurements.

Signed-off-by: Karl Palsson <redacted>