dt-bindings: hwmon: Add AST2700 compatible

dt-bindings: hwmon: Add AST2700 compatible

Adds support for the AST2700 PWM/Tach controller by extending the
compatible string enumeration in the device tree binding.

The AST2700 PWM/Tach hardware is compatible with the existing binding
schema and requires no additional properties or modifications beyond
the new compatible string.

Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20251120-upstream_pwm_tach-v3-1-eaa2f9b300a2@aspeedtech.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>