drm/amdgpu/display: Fix Pollock Variant Detection

Problem Description:
Currently we are checking internal fused rev id with pci rev id. However, fused
internal rev id is the same on all raven2 parts (in which Dali and Pollock were
based on too), thus Pollock detection fails

Fix:
use the pci rev to preform the detection for bandwidth calculations.

Reviewed-by: Feifei Xu <Feifei.Xu@amd.com>
Signed-off-by: Aly-Tawfik <altawfik@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>