Add experimental double FPS mode for OV2640

Allows for 52fps@CIF, 26fps@SVGA and 6.5fps@UXGA (unchanged) when XCLK is set to 10MHz

driver/camera.c

@@ -884,6 +884,7 @@ esp_err_t camera_probe(const camera_config_t* config, camera_model_t* out_camera
         return ESP_ERR_CAMERA_NOT_DETECTED;
     }
     s_state->sensor.slv_addr = slv_addr;
+    s_state->sensor.xclk_freq_hz = config->xclk_freq_hz;
 
     //s_state->sensor.slv_addr = 0x30;
     ESP_LOGD(TAG, "Detected camera at address=0x%02x", s_state->sensor.slv_addr);