scsi: ufshcd: Allow specifying an Auto-Hibernate Timer value of zero

scsi: ufshcd: Allow specifying an Auto-Hibernate Timer value of zero

Setting the Auto-Hibernate Timer to zero is a valid setting which indicates
the Auto-Hibernate feature being disabled. Correctly support this setting.

In addition, when the timer value is queried from sysfs, read from the host
controller's register and return that value instead of using the RAM value.

Link: https://lore.kernel.org/r/b141cfcd7998b8933635828b56fbb64f8ad4d175.1598661071.git.nguyenb@codeaurora.org
Acked-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Bao D. Nguyen <nguyenb@codeaurora.org>
Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
Signed-off-by: Can Guo <cang@codeaurora.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>