dt-bindings: mfd: mediatek: mt6397: Convert to DT schema format

dt-bindings: mfd: mediatek: mt6397: Convert to DT schema format

Convert the mfd: mediatek: mt6397 binding to DT schema format.

MT6323, MT6358, and MT6397 are PMIC devices with multiple function
subdevices. They share a common PMIC design but have variations in
subdevice combinations.

Key updates in this conversion:

1. RTC:
   - Convert rtc-mt6397.txt and merge into parent MT6397 PMIC DT schema.

2. Regulators:
   - Align to generic name "regulators".
   - Update references from .txt to .yaml for mt6323, mt6358, and mt6397
     regulators.
   - Simplify regulator name labels in device tree examples.

3. Audio Codec:
   - Simplify Audio Codec part with updating compatible items.
   - Align to generic name "audio-codec" for codec and sound subdevices.

4. Clocks:
   - Align to generic name "clocks" for clockbuffer subdevices.

5. LEDs:
   - Convert leds-mt6323.txt and merge into parent MT6397 PMIC DT schema.
   - Update LED binding.

6. Keys:
   - Add detailed descriptions for power and home keys.
   - Add compatible: mediatek,mt6358-keys.

7. Power Controller:
   - Convert mt6323-poweroff.txt and merge into parent MT6397 PMIC DT
     schema.
   - Add #power-domain-cells property to fix dt-binding check error.
   - Clarify "BBPU" as "Baseband power up".

8. Pinctrl:
   - Align to generic name "pinctrl" instead of "pin-controller".

9. Compatible:
   - Drop "mediatek,mt6357" since there is a separated DT Schema
     for PMIC MT6357.

10. Examples:
   - MT6323: Retain complete examples for this PMIC.
   - MT6358 and MT6397: simplify settings in regulators.
    - Preserve "audio-codec", "clocks", "pinctrl", "rtc", and "keys"
      sections as they contain typical settings for different PMICs.

Additional updates:
- MAINTAINERS: Add co-maintainers and reference to
  mfd/mediatek,mt6397.yaml for LED and power-controller drivers.
- input/mediatek,pmic-keys.yaml: Update reference to
  mfd/mediatek,mt6397.yaml.

Signed-off-by: Sen Chu <sen.chu@mediatek.com>
Signed-off-by: Macpaul Lin <macpaul.lin@mediatek.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20241001104145.24054-3-macpaul.lin@mediatek.com
Signed-off-by: Lee Jones <lee@kernel.org>