[PATCH v6] Add Mediatek thermal support

[Sascha Hauer]

This series adds support for the thermal sensors included in the
MT8173 SoC. Currently only basic temperature reading is supported
without any interrupt support.

The cpufreq driver for MT8173 is currently under review, so there's no
real cooling device available in mainline. Until this is available the
thermal driver can be tested with the following dts snippet. It creates
a fake gpio fan and a fake trip point which is so low that it can easily
be reached with a "cat /dev/zero > /dev/null" on the command line.

Please review and let me know what's missing to be included in mainline.

changes since v5:
- update copyright
- remove unused defines

Changes since v4:
- give calibration constants more meaningful names (offset, slope)
- Use define instead of 0x00c for register access.

Changes since v3:
- add include/dt-bindings/thermal/mt8173.h for to be able to use sensor names
  in dts files
- fix disabling wrong clock in error path
- remove now unused reset-names property from binding document
- rename MT8173_NUM_BANKS -> MT8173_NUM_ZONES
- rename MT8173_NUM_SENSING_POINTS -> MT8173_NUM_SENSORS_PER_ZONE
- rename struct thermal_zone_device *tz -> struct thermal_zone_device *tzd

Changes since v2:
- sort #includes alphabetically
- Add prefix to register defines
- drop some members from struct mtk_thermal
- simplify raw_to_mcelsius()
- add and use more register bit defines
- use device_reset() instead of devm_reset_control_get()/reset_control_reset()
- misc other stuff

Changes since v1:
- Use "mediatek," prefix for custom properties
- Drop "thermal: consistently use int for temperatures" dependency

Sascha

        fan: gpio_fan {
                compatible = "gpio-fan";
                gpios = <&pio 24 0>;
                gpio-fan,speed-map = <0    0
                                      4500 1>;
                #cooling-cells = <2>;
        };

        thermal-zones {
                cpu_thermal: cpu_thermal {
                        polling-delay-passive = <1000>; /* milliseconds */
                        polling-delay = <1000>; /* milliseconds */

                        thermal-sensors = <&thermal 0>;

                        trips {
                                cpu_passive: cpu_passive {
                                        temperature = <47000>; /* millicelsius */
                                        hysteresis = <2000>; /* millicelsius */
                                        type = "passive";
                                };

                                cpu_crit {
                                        temperature = <90000>; /* millicelsius */
                                        hysteresis = <2000>; /* millicelsius */
                                        type = "critical";
                                };
                        };

                        cooling-maps {
                                map0 {
                                        trip = <&cpu_passive>;
                                        cooling-device = <&fan THERMAL_NO_LIMIT THERMAL_NO_LIMIT>;
                                };
                        };
                };
        };