ARM: SPEAr: DT: add uart state to fix warning

amba-pl011 driver supports two pin state "default" and "sleep" and it
expect from dt to provide this pinctrl states and phandler otherwise it
gives a warning message.

To remove this warning message pass default state with null phandler to uart
pins in device node (In our case all the pins are configured in default states
so we pass null phandler to pins).

Signed-off-by: Vipul Kumar Samar <vipulkumar.samar@st.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>