thermal/drivers/st: Remove syscfg based driver

The syscfg based thermal driver is only supporting STiH415 STiH416 and
STiD127 platforms which are all no more supported.  We can thus safely
remove this driver since the remaining STi platform STiH407/STiH410
and STiH418 are all using the memmap based thermal driver.

Signed-off-by: Alain Volmat <avolmat@me.com>
Link: https://lore.kernel.org/r/20230209091659.1409-7-avolmat@me.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>