drm/radeon: Fix off-by-one errors in radeon_vm_bo_set_addr

eoffset is sometimes treated as the last address inside the address
range, and sometimes as the first address outside the range. This
was resulting in errors when a test filled up the entire address
space. Make it consistent to always be the last address within the
range. Also fixed related errors when checking the VA limit and in
radeon_vm_fence_pts.

Signed-off-by: Felix.Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: stable@vger.kernel.org