component/bt: bugfix of bluetooth modem sleep not being able to work with Dynamic Frequency Scaling

1. start an esp_timer on entering sleep to acquire pm_lock before wake up from modem sleep
2. decrease the clock division of XTAL fed to bluetooth low power clock from 32us to 2us period to allow to work under 240MHz Max CPU frequency
3. decrease the minimum sleep duration threshold to allow shorter bluetooth modem sleep period, especially for BLE with short connection interval
4. reconfigure bluetooth baseband(BT-BB) settings after PHY/RF init upon waking up from modem sleep to avoid packet RX/TX performance degradation

components/esp32/include/esp_phy_init.h

@@ -226,6 +226,12 @@ esp_err_t esp_modem_sleep_register(modem_sleep_module_t module);
  */
 esp_err_t esp_modem_sleep_deregister(modem_sleep_module_t module);
 
+/**
+ * @brief            Get the time stamp when PHY/RF was switched on
+ * @return           return 0 if PHY/RF is never switched on. Otherwise return time in
+ *                   microsecond since boot when phy/rf was last switched on
+*/
+int64_t esp_phy_rf_get_on_ts(void);
 #ifdef __cplusplus
 }
 #endif