Export ufshcd_hba_stop() to allow vendors to disable HCI in variant ops.

Link: https://lore.kernel.org/r/20210528033624.12170-2-alice.chao@mediatek.comReviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Alice.Chao <alice.chao@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>