dmaengine/dw_dmac: Hibernation support in dw_dmac

The suspend and resume implementation is through dev_pm_ops in dmac. So
in order to support hibernation, freeze, thaw, restore and poweroff
features are required.

Signed-off-by: Rajeev Kumar <rajeev-dlh.kumar@st.com>
Acked-by: Viresh Kumar <viresh.kumar@st.com>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>