drm/amdkfd: Update number of compute unit from KGD

Overwrite the active simd_count from KGD at driver loading time. This is
based on assumption that register GC_USER_SHADER_ARRAY_CONFIG won’t get
changed.

V2: remove the incorrect simd_count reported at loading module.

Signed-off-by: Flora Cui <flora.cui@amd.com>
Reviewed by: Yair Shachar< yair.shachar@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>