drm/amdgpu/vpe: remove IB end boundary requirement

Remove IB end boundary requirement,
VPE has no such limitions, use existing
amdgpu_ring_generic_pad_ib() instead.
This is missed in rebase.

Signed-off-by: Lang Yu <Lang.Yu@amd.com>
Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>