Function esp_idf_sys::ets_get_xtal_freq

pub unsafe extern "C" fn ets_get_xtal_freq() -> u32

@brief Get xtal_freq value, If value not stored in RTC_STORE5, than store.

@param None

@return uint32_t : if stored in efuse(not 0) clock = ets_efuse_get_xtal_freq() * 1000000; else if analog_8M in efuse clock = ets_get_xtal_scale() * 625 / 16 * ets_efuse_get_8M_clock(); else clock = 40M.