Customize the WCDMA signal strength based on RSCP

To customize the WCDMA signal strength based on RSCP, acquire RSCP of
WCDMA from RIL and set it in signal strength.

Test: manual - Checked that signal bar of WCDMA signal strength can be
customized based on RSCP.
Test: auto - Passed SignalStrengthTest and ServiceStateTrackerTest.
Bug: 71329173
Change-Id: Ifdea81c7a6968fda7236663b6ebb0a8be7f64fb1