scsi: ufs: Introduce vops for resetting device

Some UFS memory devices needs their reset line toggled in order to get
them into a good state for initialization. Provide a new vops to allow
the platform driver to implement this operation.

Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Reviewed-by: Bean Huo <beanhuo@micron.com>
Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>