docs: rename amdgpu_plugin.txt to criu-amdgpu-plugin.txt
By default, the file name 'amdgpu_plugin.txt' is used also as the name
for the corresponding man page (`man amdgpu_plugin`). However, when
this man page is installed system-wide it would be more appropriate
to have a prefix 'criu-' (e.g., `man criu-amdgpu-plugin`).
Signed-off-by: Radostin Stoyanov <[email protected]>