stv0991: configure clock & pad muxing for qspi

stv0991 has cadence qspi controller for flash interfacing, this
patch configures the device pads & clock for the controller.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
Reviewed-by: Jagannadh Teki <jteki@openedev.com>