[LinuxPPS] ntp: add hardpps implementation

[Remco dB]

OK, 

I applied the latest Alex-patch on kernel-2.6.34 and got 'it' working 
according to Udo's howto on the PPS wiki. 

Interestingly, when I perform a ntpdc -c kern <LinuxPPS machine with hardpps> 
the PLL offset remains rock solid 0 sec. 
Status now is 0x2107 instead of 0x2007 or 0x2001.

However, when I do a ntpq -p the offset remains .. rock solid 127 us. 
When I do not use hardpps the system behaves more 'normal' and displays
with a ntpq -p query to an offset of +/- 0.001 on the same system.

PLL freq without hardpps is 157 ppm and with hardpps 30 ppm.

I remember that there was an issue with CONFIG_NO_HZ. 
In my current hardpps kernel CONFIG_NO_HZ is set (y). 
Considering the 'rock solid' offset of 127 us, should I change this to 'n' ?

Remco