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
5. Fix potential memory leak