Bug#939781: Please include Navi10 firmware files

[at46]

Since we have mesa, libdrm and kernel with Navi 10 support in Debian 
now, it would be nice to also have the firmware files available direct. 
They were added to the kernel archive at october 23rd 
(https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git/commit/?id=417a9c6e197a8d3eec792494efc87a2b42f76324).

Axel