ata: libata-eh: Update DIPM comments to reflect reality

The comments describing which LPM policies that has DIPM enabled predates
the introduction of the LPM policies ATA_LPM_MIN_POWER_WITH_PARTIAL and
ATA_LPM_MED_POWER_WITH_DIPM. Update the DIPM comments to reflect reality.

Also remove the sentence that claims that "Order device and link
configurations such that the host always allows DIPM requests."

This comment is written before 24e0e61d ("ata: libata: disallow
dev-initiated LPM transitions to unsupported states").

Even though the set_lpm() call is done before enabling DIPM, the host will
not always allow DIPM requests. For all LPM polcies where DIPM is enabled,
only DIPM requests to LPM states that are supported by the HBA will be
allowed.

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