net: pse-pd: pd692x0: Preserve PSE configuration across reboots

net: pse-pd: pd692x0: Preserve PSE configuration across reboots

Detect when PSE hardware is already configured (user byte == 42) and
skip hardware initialization to prevent power interruption to connected
devices during system reboots.

Previously, the driver would always reconfigure the PSE hardware on
probe, causing a port matrix reflash that resulted in temporary power
loss to all connected devices. This change maintains power continuity
by preserving existing configuration when the PSE has been previously
initialized.

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20251013-feature_pd692x0_reboot_keep_conf-v2-3-68ab082a93dd@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>