drm/amdgpu: Adjust error inject function code style in amdgpu_ras.c

1. Move xgmi special error inject function from amdgpu_ras.c to xgmi block.
2. Support to use psp_ras_trigger_error as default error inject function in amdgpu_ras.c. If .ras_error_inject isn't defined in ras block, default error inject function will take effect.

v2: squash in warning fix (Alex)

Signed-off-by: yipechai <YiPeng.Chai@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: John Clements <john.clements@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>