drm/amdgpu: add module parameter choose reset mode

Default value is auto, doesn't change
original reset method logic.

v2: change to use parameter reset_method
v3: add warn msg if specified mode isn't supported

Signed-off-by: Likun Gao <Likun.Gao@amd.com>
Signed-off-by: Wenhui Sheng <Wenhui.Sheng@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>