Replace suggestion API flag with UI flag

We should have two flags for suggestion changes. The API flag should be
used to control the rollout of the API itself, while the UI flag should
be to guard UI changes.

Test: atest
Bug: 411452237
Flag: com.android.systemui.enable_suggested_device_ui
Change-Id: I49e5ac959e818145be61d02db13a717b2c485c89