drm/amd/powerplay: revise the way to retrieve the board parameters

It can support different NV1x ASIC better. And this can guard
no member got missing.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Kenneth Feng <kenneth.feng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>