ata: libata-sata: improve sysfs description for ATA_LPM_UNKNOWN

Currently, both ATA_LPM_UNKNOWN (0) and ATA_LPM_MAX_POWER (1) displays
as "max_performance" in sysfs.

This is quite misleading as they are not the same.

For ATA_LPM_UNKNOWN, ata_eh_set_lpm() will not be called at all,
leaving the configuration in unknown state.
For ATA_LPM_MAX_POWER, ata_eh_set_lpm() is called, and setting the
policy to ATA_LPM_MAX_POWER.

This also matches the description of the SATA_MOBILE_LPM_POLICY Kconfig:
0 => Keep firmware settings
1 => Maximum performance

Thus, update the sysfs description for ATA_LPM_UNKNOWN to match reality.

While at it, update libata.h to mention that the ascii descriptions
are in libata-sata.c and not in libata-scsi.c.

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