rename arch specific bitdepth template files

Missed in 46e2a2d0. Arm asm will be hard to template so move them to
the plain source list.

Fix #96.
8 jobs for master in 3 minutes and 43 seconds (queued for 24 seconds)
Status Job ID Name Coverage
  Build
passed build-debian #5729
amd64 debian

00:00:31

passed build-debian-aarch64 #5733
debian aarch64

00:01:17

passed build-debian-aarch64-clang-5 #5734
debian clang5 aarch64

00:01:09

passed build-debian-static #5730
amd64 debian

00:00:30

passed build-debian-werror #5736
debian aarch64

00:01:02

passed build-macos #5735
macos

00:00:24

passed build-win32 #5731
win32

00:00:27

passed build-win64 #5732
win64

00:00:33