ptp: Added a brand new class driver for ptp clocks.

ptp: Added a brand new class driver for ptp clocks.

This patch adds an infrastructure for hardware clocks that implement
IEEE 1588, the Precision Time Protocol (PTP). A class driver offers a
registration method to particular hardware clock drivers. Each clock is
presented as a standard POSIX clock.

The ancillary clock features are exposed in two different ways, via
the sysfs and by a character device.

Signed-off-by: Richard Cochran <[email protected]>
Acked-by: Arnd Bergmann <[email protected]>
Acked-by: David S. Miller <[email protected]>
Signed-off-by: John Stultz <[email protected]>