ata: ahci: Rename CONFIG_SATA_LPM_MOBILE_POLICY configuration item

`CONFIG_SATA_LPM_MOBILE_POLICY` reflects a configuration to apply only to
mobile chipsets.  As some desktop boards may want to use this policy by
default as well, rename the configuration item to `SATA_LPM_POLICY`.

Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>