ptp: Added a clock driver for the IXP46x.

This patch adds a driver for the hardware time stamping unit found on the
IXP465. The basic clock operations and an external trigger are implemented.

Signed-off-by: Richard Cochran <richard.cochran@omicron.at>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: John Stultz <john.stultz@linaro.org>
Acked-by: Krzysztof Halasa <khc@pm.waw.pl>
Signed-off-by: John Stultz <john.stultz@linaro.org>