drm/amdgpu: Refactor VCN v5.0.1 HW init into separate instance function

drm/amdgpu: Refactor VCN v5.0.1 HW init into separate instance function

Split the per-instance initialization code from vcn_v5_0_1_hw_init()
into a new vcn_v5_0_1_hw_init_inst() function. This improves code
organization by:

1. Separating the instance-specific initialization logic
2. Making the main init function more readable
3. Following the pattern used in queue reset

The SR-IOV specific initialization remains in the main function since
it has different requirements.

Reviewed-by: Sonny Jiang <sonny.jiang@amd.com>
Signed-off-by: Jesse Zhang <Jesse.Zhang@amd.com>
Signed-off-by: Ruili Ji <ruiliji2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>