drivers: eth: e1000: Add simulated PTP clock device

For testing purposes, add simulated PTP clock device to e1000
Ethernet driver that is used in qemu_x86 board. The PTP clock
does nothing useful as there is no real hw behind this device.
We just emulate the clock in order to do some SO_TXTIME testing.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>