drivers/thermal/spear_thermal.c: add Device Tree probing capability

SPEAr platforms now support DT and so must convert all drivers to support
DT.  This patch adds DT probing support for SPEAr thermal sensor driver
and updates its documentation too.

Also, as SPEAr is the only user of this driver and is only available with
DT, make this an only DT driver.  So, platform_data is completely removed
and passed via DT now.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@st.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>