sdm_channel_enable() function

- ESP_OK: Enable SDM channel successfully - ESP_ERR_INVALID_ARG: Enable SDM channel failed because of invalid argument - ESP_ERR_INVALID_STATE: Enable SDM channel failed because the channel is already enabled - ESP_FAIL: Enable SDM channel failed because of other error

This function will transit the channel state from init to enable. This function will acquire a PM lock, if a specific source clock (e.g. APB) is selected in the `sdm_config_t`, while `CONFIG_PM_ENABLE` is enabled.