Only notify SIM state changes when it has actually changed

onSubscriptionInfoChanged gets called quite frequently whenever
something about the connectivity changes, which could lead that the
whole state of the Keyguard was reset. This change actually checks
whether the state has really changed and thus only resets Keyguard
when necessary.

Bug: 18821582
Change-Id: Ia70804d0337b11914c7d57aa4cdc47d585786f1d