scsi: dt-bindings: ufs: Add sm8150 compatible string

Document "qcom,sm8150-ufshc" compatible string for UFS HC found on SM8150.

Link: https://lore.kernel.org/r/20191024074802.26526-2-vkoul@kernel.org
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>