Fix iwlwifi driver failing to find .pnvm files for Intel 6E (AX210)

Since updating to Buildroot 2024.02, the iwlwifi loads a different version of
firmware for Intel AX cards (reported on AX210) which also needs the pnvm file.
However, unlike firmwares, the load method is different and the driver can't
load a compressed file. Disable compression for all .pnvm files to fix this.

* buildroot baa16784d2...55be56d521 (1):
  > package/linux-firmware: exclude some files from compression

Fixes #3477