drm/amd/powerplay: avoid using pm_en before it is initialized

hwmgr->pm_en is initialized at hwmgr_hw_init.
during amdgpu_device_init, there is amdgpu_asic_reset that calls to
pp_get_asic_baco_capability, while hwmgr->pm_en has not yet been initialized.

so avoid using pm_en in pp_get_asic_baco_capability.

Reviewed-by: Emily Deng <Emily.Deng@amd.com>
Signed-off-by: Tiecheng Zhou <Tiecheng.Zhou@amd.com>
Signed-off-by: Yintian Tao <yttao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>