Kernel 4.14-rc1 will soon be out, and one change is the removal of the ‘firmware’ portion of the kernel tree..   # make firmware_install will no longer work.

Apparently, this in-kernel-tree firmware has not been updated since 2013 (!) and all appropriate firmware has been supplied by the ‘linux-firmware’ distro packages for some time..

Details here:   http://lkml.iu.edu/hypermail/linux/kernel/1709.1/04650.html

Robert Gadsdon.   September 15, 2017.