drm/amdgpu/vce4: replaced with virt_alloc_mm_table

Used virt_alloc_mm_table function to allocate MM table memory.

Signed-off-by: Xiangliang Yu <Xiangliang.Yu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>