drm/amd/pm: Read BIF STRAP also for BACO check

Avoid reading BIF STRAP each time for BACO capability. Read the STRAP
value while checking BACO capability in PPTable.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>