drm/amdgpu: ih doorbell size of range changed for nbio v7.4
[Why]
nbio v7.4 size of ih doorbell range is 64 bit. This requires 2 DWords per register.
[How]
Change ih doorbell size from 2 to 4. This means two Dwords per ring.
Current configuration uses two ih rings.
Signed-off-by: Alex Sierra <alex.sierra@amd.com> Acked-by: Alex Deucher <alexander.deucher@amd.com> Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>