thermal: ti-soc-thermal: Use GPIO descriptors

This switches the TI SoC thermal driver to use GPIO
descriptors instead of retrieveing a GPIO number from the
device tree and requesting the GPIO separately.

Cc: Keerthy <j-keerthy@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200229210532.173430-1-linus.walleij@linaro.org