Expose ModemActivitiyInfo to system API

ModemActivityInfo is used for batteryStatusService which is part of
system service. To prepare telephony to be an mainline module, we
should expose ModemActivityInfo to systemAPI

1. remove getConsumedPower API as we are missing modem support, API
today only report 0
2. isValid API is introduced to cover modem issues before. Do not
expose this for now.

Bug: 140908357
Test: Build
Change-Id: I6e1b0daa2e0ce23b9fd55f0dd7037631b93eb7a5