ramips: several fixes for HC5x61

 - Mark other partitions as read-only for HC5x61

 - Only enable USB and PCIe for HC5761/HC5861
   HC5661 doesn't have a USB port, and there is nothing attached to its PCIe.

 - Fix HC5761 switch ports
   HC5761 has only 3 ethernet ports (1x WAN + 2x LAN). Remove unused ports.

 - Fix HC5861 5GHz radio
   HC5861 has MT7612EN 5GHz WiFi chip, not MT7610EN.

 - Fix HC5761/HC5861 WiFi LEDs
   After 5GHz is enabled, it becomes wlan0. And 2.4GHz would be wlan1.

 - Fix HC5x61 image size
   It should be 15872k (0xf80000)

Signed-off-by: Deng Qingfang <dengqf6@mail2.sysu.edu.cn>