drm/amdgpu: Add missing power attribute to APU check

[ Upstream commit dc14eb12f6bb3e779c5461429c1889a339c67aab ]

Add missing power_average to visible check for power
attributes for APUs.  Was missed before.

Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>