tg3: PTP - Implement the ptp api and ethtool functions

This patch adds the ptp_caps structure, ptp api implementation,
reference clock read and register/unregister functions.  All the basic
clock operations as described in Documentation/ptp/ptp.txt are
supported.

Frequency adjustment is performed using hardware with a 24 bit
accumulator and a programmable correction value. On each clk, the
correction value gets added to the accumulator and when it overflows,
the time counter is incremented/decremented and the accumulator reset.

So conversion from ppb to correction value is
	ppb * (1 << 24) / 1000000000

[Re-organized to put the ptp_clock_info struct declaration in one patch,
 added ptp_clock_info.name, and added locking to tg3_ptp_adjtime() based
 on input from Richard Cochran.]

Signed-off-by: Nithin Nayak Sujir <nsujir@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>