drm/amdgpu/vcn1.0: use its own idle handler and begin use funcs

Because VCN1.0 power management and DPG mode are managed together with
JPEG1.0 under both HW and FW, so separated them from general VCN code.
Also the multiple instances case got removed, since VCN1.0 HW just have
a single instance.

v2: override work func with vcn1.0's own

Signed-off-by: Leo Liu <leo.liu@amd.com>
Reviewed-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>