net: cavium: Fix build errors due to 'imply CAVIUM_PTP'

If CAVIUM_PTP is m and THUNDER_NIC_VF is y, build fails:

drivers/net/ethernet/cavium/thunder/nicvf_main.o: In function 'nicvf_remove':
nicvf_main.c:(.text+0x1f0): undefined reference to 'cavium_ptp_put'
drivers/net/ethernet/cavium/thunder/nicvf_main.o: In function `nicvf_probe':
nicvf_main.c:(.text+0x557c): undefined reference to 'cavium_ptp_get'

THUNDER_NIC_VF imply CAVIUM_PTP, which allow the config now,
Use IS_REACHABLE() to avoid the vmlinux link error for this case.

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: def2fbffe62c ("kconfig: allow symbols implied by y to become m")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net: cavium: Use the correct style for SPDX License Identifier

This patch corrects the SPDX License Identifier style
in header files related to Cavium Ethernet drivers.
For C header files Documentation/process/license-rules.rst
mandates C-like comments (opposed to C source files where
C++ style should be used)

Changes made by using a script provided by Joe Perches here:
https://lkml.org/lkml/2019/2/7/46.

Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Nishad Kamdar <nishadkamdar@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net: add support for Cavium PTP coprocessor

This patch adds support for the Precision Time Protocol
Clocks and Timestamping hardware found on Cavium ThunderX
processors.

Signed-off-by: Radoslaw Biernacki <rad@semihalf.com>
Signed-off-by: Aleksey Makarov <aleksey.makarov@cavium.com>
Acked-by: Philippe Ombredanne <pombredanne@nexb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>