drm/amdgpu: revert "rework reserved VMID handling" v2

drm/amdgpu: revert "rework reserved VMID handling" v2

This reverts commit e44a0fe630c58b0a87d8281f5c1077a3479e5fce.

Initially we used VMID reservation to enforce isolation between
processes. That has now been replaced by proper fence handling.

Both OpenGL, RADV and ROCm developers requested a way to reserve a VMID
for SPM, so restore that approach by reverting back to only allowing a
single process to use the reserved VMID.

Only compile tested for now.

v2: use -ENOENT instead of -EINVAL if VMID is not available

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>