ethernet: fix some bugs in phy&mac driver

1. Original register mapping for LAN8720 has some registers that doesn't exist/support.
So just remove them, and fix the power and init function for LAN8720.
2. GPIO16 and GPIO17 is occupied by PSRAM, so only ETH_CLOCK_GPIO_IN mode is supported in that case if using PSRAM.
3. Fix bug of OTA failing with Ethernet
4. Fix bug of multicast with Ethernet

Closes https://github.com/espressif/esp-idf/issues/2564
Closes https://github.com/espressif/esp-idf/issues/2620
Closes https://github.com/espressif/esp-idf/issues/2657

components/esp32/include/esp_spiram.h

@@ -56,7 +56,7 @@ void esp_spiram_init_cache();
 
 /**
  * @brief Memory test for SPI RAM. Should be called after SPI RAM is initialized and
- * (in case of a dual-core system) the app CPU is online. This test overwrites the 
+ * (in case of a dual-core system) the app CPU is online. This test overwrites the
  * memory with crap, so do not call after e.g. the heap allocator has stored important
  * stuff in SPI RAM.
  *
@@ -102,4 +102,14 @@ void esp_spiram_writeback_cache();
 esp_err_t esp_spiram_reserve_dma_pool(size_t size);
 
 
+/**
+ * @brief If SPI RAM(PSRAM) has been initialized
+ *
+ * @return
+ *          - true SPI RAM has been initialized successfully
+ *          - false SPI RAM hasn't been initialized or initialized failed
+ */
+bool esp_spiram_is_initialized(void);
+
+
 #endif