ata: ahci: print the lpm policy on boot

The target LPM policy can be set using either a Kconfig or a kernel module
parameter.

However, if the board type is set to anything but board_ahci_low_power,
then the LPM policy will overridden and set to ATA_LPM_UNKNOWN.

Additionally, if the default suspend is suspend to idle, depending on the
hardware capabilities of the HBA, ahci_update_initial_lpm_policy() might
override the LPM policy to either ATA_LPM_MIN_POWER_WITH_PARTIAL or
ATA_LPM_MIN_POWER.

All this means that it is very hard to know which LPM policy a user will
actually be using on a given system.

In order to make it easier to debug LPM related issues, print the LPM
policy on boot.

One common LPM related issue is that the device fails to link up.
Because of that, we cannot add this print to ata_dev_configure(), as that
function is only called after a successful link up. Instead, add the info
using ata_port_desc(), with the help of a new ata_port_desc_misc() helper.
The port description is printed once per port during boot.

Before changes:
ata1: SATA max UDMA/133 abar m524288@0xa5780000 port 0xa5780100 irq 170
ata2: SATA max UDMA/133 abar m524288@0xa5780000 port 0xa5780180 irq 170

After changes:
ata1: SATA max UDMA/133 abar m524288@0xa5780000 port 0xa5780100 irq 170 lpm-pol 4
ata2: SATA max UDMA/133 abar m524288@0xa5780000 port 0xa5780180 irq 170 lpm-pol 4

Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>