runtime_tunables: Add runtime pm enabling support for ahci

Add runtime pm enabling support for SATA/AHCI based systems. This patch
enables runtime pm for all the ports that are supported by SATA and the
disk.

Runtime pm enabling support for host i.e., SATA itself is already
included.

Signed-off-by: Gayatri Kammela <gayatri.kammela@intel.com>