drm/amdgpu: Query ras capablity from psp v2

Instead of traditional atomfirmware interfaces for RAS
capability, host driver can query ras capability from
psp starting from psp v13_0_6.

v2: drop redundant local variable from get_ras_capability.

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>