octeontx2-bphy-netdev: convert MIO_PTP_TIMESTAMP value to nsecs

commit 0c135c5a8505e53399513baa5939c37726a3956e from
git@git.assembla.com:cavium/WindRiver.linux.git

MIO_PTP_TIMESTAMP register format is <31:0> NANOSEC, <63:32> SEC.
So convert the timestamp to nanoseconds before processing.

Change-Id: Idce99ce2ef59e137ba066d58c0db2b8892c49348
Signed-off-by: Naveen Mamindlapalli <naveenm@marvell.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/86944


Reviewed-by: Rakesh Babu Saladi <rsaladi2@marvell.com>
Reviewed-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Tested-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>