net: ena: View PHC stats using debugfs

Add an entry named `phc_stats` to view the PHC statistics.
If PHC is enabled, the stats are printed, as below:

phc_cnt: 0
phc_exp: 0
phc_skp: 0
phc_err_dv: 0
phc_err_ts: 0

If PHC is disabled, no statistics will be displayed.

Signed-off-by: David Arinzon <darinzon@amazon.com>
Link: https://patch.msgid.link/20250617110545.5659-9-darinzon@amazon.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>