thermal/drivers/rockchip: Support dynamic sized sensor array

Dynamically allocate the sensors array based on the amount
of platform sensors in preparation for rk3588 support, which
needs 7 sensors.

Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20230308112253.15659-6-sebastian.reichel@collabora.com