LKM Timemark Driver

[MLewis]

I've put my fancy do everything LKM Timemark driver tool on hold.
Instead, I robbed that code to work towards a robust LKM Timemark Echo 
more suitable for use in making an ntpsec clock driver.

As was suggested to me, the timestamp of the outgoing Timemark trigger 
pulse is bracketed, a timespec tv_pre set and a timespec tv_post set. 
You can monitor their width, calculate an 'actual', use a Kalman filter 
or just use the post timestamp. Includes a sequence number.

Pulse width can be specified, and the pulse can be set to be Positive or 
Negative.

Three modes, Timemark pulse goes out upon:
- receiving a PPS (echo)
- timed to trigger at x ms past system time TOS (no PPS required)
- timed to trigger every x ms (no PPS required)(someone wants to be able 
to trigger at a spacing a little more than a whole second)

It's coming along nicely and may be released this week.

Single outgoing port for now, so only one Timemark can be driven for 
those modules that have more.

It will do what the ublox M8 series need, as that's what I have and can 
test against it. I hope that features can be added to allow other module 
types to be driven.

As it's a LKM, anyone can mod it to their needs, load and run it, 
without needing a system patch.

Have I missed any obvious driver features?

Michael