scsi: ufs: Introduce ufshcd_get_pwr_dev_param

ufshcd_get_pwr_dev_param defines an interface for power mode management
currently used by both ufs-qcom and ufs-hisi. Move the interface to ufs
core so every driver can take advantage of it.

Signed-off-by: Stanley Chu <stanley.chu@mediatek.com>
Reviewed-by: Avri Altman <avri.altman@wdc.com>
Acked-by: Bean Huo <beanhuo@micron.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>