MSIM: behave as single SIM when appropriate

On 'About phone' multi-SIM devices show network info for each SIM
slot even if there's no SIM available. With this change, if the
device has less than two SIMs it behaves as a single SIM device.

Change-Id: Id45b8f7b1b3f7d47b882e49ccaf35ac28561a57f