kernel: include wireless regulatory db in firmware

[greatgitsby]

Summary

• Embed regulatory.db and regulatory.db.p7s into the kernel image via CONFIG_EXTRA_FIRMWARE
• cfg80211 is built-in (CONFIG_CFG80211=y), so it requests the regulatory database before the rootfs is mounted — causing the firmware load to fail

Device logs

Before (regulatory.db fails to load):

[    5.338050] cfg80211: Loading compiled-in X.509 certificates for regulatory database
[    5.364903] faux_driver regulatory: Direct firmware load for regulatory.db failed with error -2
[    5.373691] cfg80211: failed to load regulatory.db
[    5.485407] VFS: Mounted root (ext4 filesystem) readonly on device 8:6.

After (loads successfully):

[    5.316133] cfg80211: Loading compiled-in X.509 certificates for regulatory database

Why

The regulatory database file exists in the rootfs (installed by the wireless-regdb package), but cfg80211 is built into the kernel and tries to load it ~120ms before the root filesystem is mounted. Embedding the files via CONFIG_EXTRA_FIRMWARE makes them available as built-in firmware blobs, independent of rootfs mount timing.

Test plan

• Flash kernel to comma tizi and mici
• Verify regulatory.db error no longer appears in dmesg