drm/amdgpu: remove the dummy fn acp_early_init

acp_early_init is a dummy function and is not being
used and hence removed.

Signed-off-by: Sunil Khatri <sunil.khatri@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>