ptp: rework gianfar_ptp as QorIQ common PTP driver

gianfar_ptp was the PTP clock driver for 1588 timer
module of Freescale QorIQ eTSEC (Enhanced Three-Speed
Ethernet Controllers) platforms. Actually QorIQ DPAA
(Data Path Acceleration Architecture) platforms is
also using the same 1588 timer module in hardware.

This patch is to rework gianfar_ptp as QorIQ common
PTP driver to support both DPAA and eTSEC. Moved
gianfar_ptp.c to drivers/ptp/, renamed it as
ptp_qoriq.c, and renamed many variables. There were
not any function changes.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>