Add SettingsSpinnerPreference#setClickable

This change add the API for Storage Settings to set
the spinner not clickablewhen there is only 1 volume.

Bug: 187801712
Test: manual
      Click the spinner when there is only default volume.
      Click the spinner when there is USB drive connected.
Change-Id: I1e6d46c9772b641678085d41d4905022e893acc4