In CarrierTextController replace getPhoneCount with getMaxPhoneCount.

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.

Bug: 141388730
Test: unittest and manual

Change-Id: I141689fc55063d87f4f7e5c605a461517beeabe4
Merged-In: I141689fc55063d87f4f7e5c605a461517beeabe4