drm/amdgpu: adding device coredump support

Added device coredump information:
- Kernel version
- Module
- Time
- VRAM status
- Guilty process name and PID
- GPU register dumps
v1 -> v2: Variable name change
v1 -> v2: NULL check
v1 -> v2: Code alignment
v1 -> v2: Adding dummy amdgpu_devcoredump_free
v1 -> v2: memset reset_task_info to zero
v2 -> v3: add CONFIG_DEV_COREDUMP for variables
v2 -> v3: remove NULL check on amdgpu_devcoredump_read

Signed-off-by: Somalapuram Amaranath <Amaranath.Somalapuram@amd.com>
Reviewed-by: Shashank Sharma <Shashank.sharma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>