Add telephony sources to hiddenapi-mappings

This makes it possible to annotate telephony greylisted apis in
frameworks/opt/telephony.

Test: m hiddenapi-mappings
Bug: 110868826

(cherry picked from commit 6dd843a6)

Change-Id: Ie6652ad1c6ef054a11f0341d7f53f3b8aec988ae
Merged-In: I1f7d2722bd7621c9f6d1195ea212a7a0454d560d