liquidio: moved ptp_enable to octeon_device structure

ptp_enable was a global static variable.  Moved this global variable to
octeon_device structure and removed extra device id check.

Signed-off-by: Intiyaz Basha <intiyaz.basha@cavium.com>
Signed-off-by: Felix Manlunas <felix.manlunas@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>