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: NRichard Cochran <richard.cochran@omicron.at>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>