Set isGsm flag based on currently camped voice and data RATs

Use currently camped RATs to determine isGsm the flag
instead of checking both phone type and camped RATs.

Test: Verified the signal bar for the following use cases
Idle:
 - SRLTE (1x & LTE) mode
 - hVoLTE mode
 - 2G only, 3G preferred, LTE preferred
 - Cellular and IWLAN registered

Voice calls:
 - CS calls on 1x, GSM, UMTS for all possible voice, data RATs
 - IMS calls on LTE and IWLAN for all possible voice, data RATs

Bug: 36644977
Change-Id: Ifd996a2c902c7238f7328a42f0401c8d626e89e4