A build flag to disable phone signal strength indicators.

This uses the post-Service Level Connection command
AT+BIA to turn off the indicators.  By default it enables
all the indicators that are sent by the AG device, but this
change keeps the signal strength indicator bit set to 0.

See b/157935962 for HCI logs and analysis.

Bug: 157935962
Bug: 199827901
Tag: #security
Test: gd/cert/run
Change-Id: Iac2283440175cf42a3373f67c98ef2eb13b5f880
(cherry picked from commit 153615661a7f084081cbcc7e014a3ab18c4981ca)