These packages are subsets of sys-kernel/linux-firmware (which we do badly, see bug 613746, among others). No point in them existing.
Ideally it would be nice if sys-kernel/linux-firmware had USE flags for all the stuff it installs. I need a small subset and it installs allot and doubles the size of the files on my / partition. Even worse for some systems causes it to fill up root. Without root has plenty of space left and will never get close to maxing out. I understand it will take work to add such USE flags for all the firmware shipped. Mostly done by vendor, not per firmware flags. This package would become like a radeon USE flag. I also use broadcom stuff, so that could be another. It would still install more firmware than I need, but its less than all of the firmware.
Use linux-firmware USE=savedconfig functionality if this is important for you. Depending on how that works, might miss newer versions of firmware.
commit 7df2005c25b0046a63ff03757955190f07a3cedb Author: Matt Turner <mattst88@gentoo.org> Date: Sun May 28 20:29:15 2017 -0700 package.mask: Remove mask for dropped radeon-ucode and amdgpu-ucode Bug: https://bugs.gentoo.org/614218 commit f69369ea6bade89ed36a097cab675d0c49a343fc Author: Matt Turner <mattst88@gentoo.org> Date: Sun May 28 20:28:30 2017 -0700 sys-firmware/amdgpu-ucode: Remove package Bug: https://bugs.gentoo.org/614218 commit 9960002903f3baeca80f065624b5f2986869e5b3 Author: Matt Turner <mattst88@gentoo.org> Date: Sun May 28 20:27:31 2017 -0700 sys-firmware/radeon-ucode: Remove package Bug: https://bugs.gentoo.org/614218