package/linux-firmware: add missing symlinks

As of upstream commit 9cfefbd7fbdaa5ae769e3061c463f8345d146fb7
we must manually create symlinks as they are no longer present
in the archive but created at installation.

Fixes:
    http://autobuild.buildroot.net/results/46fdacbe4064d72aaafa9f52741121d8e4fe64ab/



Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>