drm/amdgpu:Remove sdma halt/unhalt during frontdoor load

sdma halt/unhalt is performed by psp when frontdoor
loading used,so this can be skipped.

v2: Instead of removing halt/unhalt completely,
    driver will do it only during backdoor load.

Signed-off-by: Mangesh Gadre <Mangesh.Gadre@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Asad Kamal <asad.kamal@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>