eth: fbnic: Move hw_stats_lock out of fbnic_dev

eth: fbnic: Move hw_stats_lock out of fbnic_dev

Move hw_stats_lock out of fbnic_dev to a more appropriate struct
fbnic_hw_stats since the only use of this lock is to protect access to
the hardware stats. While at it, enclose the lock and stats
initialization in a single init call.

Signed-off-by: Mohsin Bashir <mohsin.bashr@gmail.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20250825200206.2357713-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>