net/octeontx2: switch Rx timestamp to dynamic mbuf field

net/octeontx2: switch Rx timestamp to dynamic mbuf field

The mbuf timestamp is moved to a dynamic field
in order to allow removal of the deprecated static field.
The related mbuf flag is also replaced.

The registration of field and flag is done in both
otx2_nix_dev_start() and otx2_nix_timesync_enable().

The dynamic offset and flag are stored in struct otx2_timesync_info
to favor cache locality.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: David Marchand <david.marchand@redhat.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>