ARM: SPEAr: DT: Update partition info for MTD devices

This patch enhances partition information of MTD devices like fsmc-nand and
spear-smi.

Signed-off-by: Shiraz Hashim <shiraz.hashim@st.com>
Signed-off-by: Vipin Kumar <vipin.kumar@st.com>
Signed-off-by: Vipul Kumar Samar <vipulkumar.samar@st.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>