drm/amd/powerplay: enable backdoor smu fw loading (v2)

enable backdoor smu fw loading on navi10

v2: squash in define fix (Alex)

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