drm/amdgpu/uvd6: add bypass support for fiji (v3)

Handle uvd clock bypass settings as part of clockgating
setup.

v2: fix gate logic
v3: fix header include

Reviewed-by: Eric Huang <JinHuiEric.Huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>