doc: migration-guide-3.7: add MAX31790

  * ``emul_bbram_backend_api`` to :c:struct:`emul_bbram_driver_api`

  * ``usbc_ppc_drv`` to :c:struct:`usbc_ppc_driver_api`

* The driver for :dtcompatible:`maxim,max31790` got split up into a MFD and an

  actual PWM driver. Previously, an instance of this device could have been

  defined like this:

  .. code-block:: devicetree

    max31790_max31790: max31790@20 {

        compatible = "maxim,max31790";

        status = "okay";

        reg = <0x20>;

        pwm-controller;

        #pwm-cells = <2>;

    };

  This can be converted to:

  .. code-block:: devicetree

    max31790_max31790: max31790@20 {

        compatible = "maxim,max31790";

        status = "okay";

        reg = <0x20>;

        max31790_max31790_pwm: max31790_max31790_pwm {

            compatible = "maxim,max31790-pwm";

            status = "okay";

            pwm-controller;

            #pwm-cells = <2>;

        };

    };

Analog-to-Digital Converter (ADC)

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