SimSettings: Disable entry for missing sim

Clicking on a missing SIM card will show incorrect information
because the user network preference is indexed by subscription id.

This means that when the SIM is not present we cannot infer which
subscription settings we are actually showing or changing so the
whole screen is effectively useless.

This patch disables configuration entries for invalid subscriptions.

Ticket: CYNGNOS-1794
Change-Id: Ic5125f66f4cdaafe06d03b3b20b80341525d6c87