ptp_qoriq: convert to use ptp_qoriq_init/free

Moved QorIQ PTP clock initialization/free into new functions
ptp_qoriq_init()/ptp_qoriq_free(). These functions could also
be reused by ENETC PTP drvier which is a PCI driver for same
1588 timer IP block.

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