thermal: kconfig: select THERMAL_WRITABLE_TRIPS for x86 thermal

After the commit "thermal: core: Add Kconfig option to enable writable
trips", by default the trips are read only. This cause user space thermal
controllers to poll for temperature as they can't set temperature
thresholds for getting a notification via uevents. These programs use RW
trip in a zone to register thresholds. Since we need to enable the new
config introduced by above commit to allow writable trips, selecting
CONFIG_THERMAL_WRITABLE_TRIP for x86 thermal drivers.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>