libdrm/amdgpu: add new vram type (GDDR6) for navi10

AMDGPU_VRAM_TYPE_GDDR6 is a new vram type for navi10

Reviewed-by: Tim Writer <Tim.Writer@amd.com>
Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>