vega20 should use umc_info v3_3 instead of v3_1. There are
serveral versions of umc_info for vega series. Compared to
various versions of these structures, vram_info strucure is
unified for vega series. The patch switch to query mem_type
from vram_info structure for all the vega series dGPU.

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