Replace getPhoneCount with getMaxPhoneCount upon object allocation.

As first step for smooth single SIM to DSDS switch, for DSDS capable
deviced we always allocate objects as if it's in DSDS mode. For example
there will be two Phone objects.
Later we'll evaluate to make the allocations dynamic to save memory.

Bug: 141388730
Test: unittest and manual
Change-Id: I3064eb616371f60776a2930c113582562d206123