Add BPI-R3 support

[TonySamaaaa]

Have tested for 24h and not found issues.
Have not fully tested WiFi.

Code comes from:

• https://github.com/Kasazaki4090/immortalwrt-mt798x

[TonySamaaaa]

Use this configuration file to compile.

Custom configuration needs to be configured with CONFIG_TARGET_ROOTFS_PARTSIZE, otherwise the single.img image cannot be generated.

[jason-akw]

Can confirm it's working on BPI-R3, but seems like it don't have PWM fan control support and SFP not working.

[TonySamaaaa]

Can confirm it's working on BPI-R3, but seems like it don't have PWM fan control support and SFP not working.

Please try d4923df27d0ea97281c33c93b47e1ec1141b7a8a.
Test pwm fan is working normally now, but you should select kmod-hwmon-pwmfan and change the thermal-zones in mt7986a.dtsi.
If sfp is not working properly you should select kmod-sfp.