Add OSMC on Raspberry Pi 4 to tested kernels

[tomhudak]

Summary

• Add kernel 5.15.92-1-osmc (OSMC on Raspberry Pi 4) to the tested kernels list
• Fix typo in uninstall note: MT7621 → MT7921

Cross-compilation notes for OSMC

OSMC on Raspberry Pi 4 runs an aarch64 kernel with armhf userland, so an aarch64 cross-compiler is required. The build also needs explicit config flags on the make command line:

make ARCH=arm64 \
    CROSS_COMPILE=aarch64-linux-gnu- \
    CONFIG_MT76_CONNAC_LIB=m \
    CONFIG_MT7921_COMMON=m \
    CONFIG_MT7921U=m
sudo make ARCH=arm64 \
    CROSS_COMPILE=aarch64-linux-gnu- \
    CONFIG_MT76_CONNAC_LIB=m \
    CONFIG_MT7921_COMMON=m \
    CONFIG_MT7921U=m \
    modules_install
sudo /sbin/depmod -a

CONFIG_MT76_CONNAC_LIB=m is critical — without it mt76-connac-lib.ko won't be built and loading the driver fails with "Unknown symbol" errors.

On OSMC, the cross-compiler is provided by the aarch64-toolchain-osmc package. Wrapper scripts are needed since the toolchain binaries live inside a chroot. Kernel headers/source (rbp464-headers-sanitised-* / rbp464-source-*) must also be installed and linked to /lib/modules/<version>/build.

Test

• Built and loaded mt7921u on OSMC with kernel 5.15.92-1-osmc on Raspberry Pi 4
• Device Fenvi FU-AX1800 (MT7921au, USB ID 0e8d:7961) detected and connected to WiFi successfully