ata: ahci: Drop low power policy board type

The low power policy board type was introduced to allow systems
to get into deep states reliably.  Before it was introduced `min_power`
was causing problems for a number of drives.  New power policies
`min_power_with_partial` and `med_power_with_dipm` have been introduced
which provide a more stable baseline for systems.

Tested-by: Damien Le Moal <dlemoal@kernel.org>
Tested-by: Jian-Hong Pan <jhp@endlessos.org>
Acked-by: Jian-Hong Pan <jhp@endlessos.org>
Acked-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
[cassel: rebase patch and fix trivial conflicts]
Signed-off-by: Niklas Cassel <cassel@kernel.org>