drm/amdgpu: Enable seq64 manager and fix bugs

- Enable the seq64 mapping sequence.
- Fix wflinfo va conflict and other bugs.

v1:
  - The seq64 area needs to be included in the AMDGPU_VA_RESERVED_SIZE
    otherwise the areas will conflict with user space allocations (Alex)

  - It needs to be mapped read only in the user VM (Alex)

v2:
  - Instead of just one define for TOP/BOTTOM
    reserved space separate them into two (Christian)

  - Fix the CPU and VA calculations and while at it
    also cleanup error handling and kerneldoc (Christian)

Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>