* kernel: bump 5.4 to 5.4.79

* ramips: add mt7620-nand driver for NAND flash

This add the mt7620-nand driver
and enable nand ubifs for subtarget mt7620
Signed-off-by: NChen Minqiang <ptpt52@gmail.com>
Co-authored-by: NChen Minqiang <ptpt52@gmail.com>

Re-add devices: XiaoMi Wifi R3/R4/AC2100, JDCloud
Signed-off-by: NAmadeusGhost <42570690+AmadeusGhost@users.noreply.github.com>

* ramips: add xiaomi_miwifi-r3 support

Specification:
 - CPU: 580 MHz
 - Flash size: 128 MiB NAND
 - RAM size: 128 MiB DDR2
 - Wireless No1: SoC-integrated: MT7620A 2x2 MIMO 802.11b/g/n (2.4 GHz)
 - Wireless No2: On-board chip: MT7612E 2x2 MIMO 802.11a/n/ac (5 GHz)
 - Switch: MT7620 built-in 10/100 switch w/ vlan support
 - USB: 2.0 x1

Flash instructions:
 1. access ssh via https://wiki.openwrt.org/toh/xiaomi/mir3
 2. in ssh:
      nvram set flag_last_success=1
      nvram set boot_wait=on
      nvram set uart_en=1
      nvram commit
      mtd write lede-ramips-mt7620-miwifi-r3-squashfs-kernel1.bin kernel1
      mtd write lede-ramips-mt7620-miwifi-r3-squashfs-rootfs0.bin rootfs0
      reboot

If you want to revert back to stock fw while on LEDE:
  insert usb stick (FAT/FAT32) with stock fw renamed to miwifi.bin
  fw_setenv flag_last_success 0
  power off the device
  hold the reset button and power on the device, keep holding the reset button until yellow led starts blinking.
Signed-off-by: NChen Minqiang <ptpt52@gmail.com>

* ramips: add mt7620-nand driver for NAND flash

This add the mt7620-nand driver
and enable nand ubifs for subtarget mt7620
Signed-off-by: NChen Minqiang <ptpt52@gmail.com>
Co-authored-by: NChen Minqiang <ptpt52@gmail.com>