net: pse-pd: Add helper to report hardware enable status of the PI

Refactor code by introducing a helper function to retrieve the hardware
enabled state of the PI, avoiding redundant implementations in the
future.

Signed-off-by: Kory Maincent (Dent Project) <kory.maincent@bootlin.com>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/20250617-feature_poe_port_prio-v14-6-78a1a645e2ee@bootlin.com


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