packagegroup-ni-extra: add linux-firmware
packagegroup-ni-extra: add linux-firmware

Add linux-firmware to be more consistent with other Krogoth based
images.

Signed-off-by: Bill Pittman <43ac99c9c99efa205ddaaebf4c7bd970d58e135c@ni.com>

ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt,ni/meta-nilrt