scsi: ufshcd-qti: enable runtime-pm

Enable runtime power-management with an idle time of 3seconds.

Change-Id: I0716a5eca20e24cc626422b6f7f3d8f0242a50d2
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Can Guo <cang@codeaurora.org>