drm/amdgpu: refactor code to split devcoredump code

drm/amdgpu: refactor code to split devcoredump code

Refractor devcoredump code into new files since its
functionality is expanded further and better to slit
and devcoredump to have its own file.

v2: Fix the build failure caught by arm compiler
of implicit function declaration with #ifdef

v3: squash in fix for implicit declaration error

Cc: Ivan Lipski <ivan.lipski@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>