ata: ahci_tegra: disable devslp for Tegra124

Tegra124 does not support devslp and it should be disabled.

Signed-off-by: Preetham Chandru R <pchandru@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>