drm/amdgpu: Add reset_context flag for host FLR

There are other reset sources that pass NULL as the job pointer, such as
amdgpu_amdkfd_reset_work. Therefore, using the job pointer to check if
the FLR comes from the host does not work.

Add a flag in reset_context to explicitly mark host triggered reset, and
set this flag when we receive host reset notification.

Signed-off-by: Yunxiang Li <Yunxiang.Li@amd.com>
Reviewed-by: Emily Deng <Emily.Deng@amd.com>
Reviewed-by: Zhigang Luo <zhigang.luo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>