ramips: improve support for STORYLiNK SAP-G3200U3

ramips: improve support for STORYLiNK SAP-G3200U3

* Increase flash SPI frequency to 50MHz

  The maximum SPI frequency of MX25L6406EM2I is 86 MHz,
  but in this patch 50 MHz was chosen as a safe value.

* Update Ethernet MAC addresses

  Till now LAN/WAN MAC addresses were flipped
  compared to stock firmware.

* Fix Wi-Fi LEDs by adding mt76 led nodes

* Fix LAN port order

  LAN ports are in reverse order of switch ports.

* Fix the well-known "LZMA ERROR 1" error by using lzma-loader

* Set uImage name, which enables installation via stock web interface:

  1.  Upload **initramfs** image file to the web page.
  2.  Boot into OpenWrt and perform sysupgrade with sysupgrade image.

Signed-off-by: Sungbo Eo <mans0n@gorani.run>