gptimer_disable() function

- ESP_OK: Disable GPTimer successfully - ESP_ERR_INVALID_ARG: Disable GPTimer failed because of invalid argument - ESP_ERR_INVALID_STATE: Disable GPTimer failed because the timer is not enabled yet - ESP_FAIL: Disable GPTimer failed because of other error

This function will transit the timer state from "enable" to "init". This function will disable the interrupt service if it's installed. This function will release the PM lock if it's acquired in the `gptimer_enable`. Disable a timer doesn't mean to stop it. See also `gptimer_stop` for how to make the timer stop counting.