ata: libata_eh: Add debug messages to ata_eh_link_set_lpm()

ata: libata_eh: Add debug messages to ata_eh_link_set_lpm()

To facilitate field debugging of link power management related issues,
add a debug message to ata_eh_link_set_lpm() to easily track LPM policy
changes done from EH context, that is, during device scan and
revalidation, error handling, and when a policy change is issued through
a host sysfs link_power_management_policy attribute.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20250701125321.69496-11-dlemoal@kernel.org
Signed-off-by: Niklas Cassel <cassel@kernel.org>