Untill now, sg_len greater than one is not supported. This patch adds support to
do that.

Note: Still, if peripheral is flow controller, sg_len can't be greater that one.
Signed-off-by: NViresh Kumar <viresh.kumar@st.com>
Acked-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NVinod Koul <vinod.koul@intel.com>