drm/amd/pm: Clean up errors in vega20_hwmgr.h

Fix the following errors reported by checkpatch:

ERROR: open brace '{' following enum go on the same line

Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Ran Sun <sunran001@208suo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>