Fix sdk aidl include for droiddoc

Prior to this change droidstubs modules that set sdk_version
did not get framework.aidl added to its aidl includes.

Bug: 149138391
Test: patch CL in bug && m system_aidl_test-droidstubs
Change-Id: I92ab344c8a4311e10c1e5c8ebf525fa2dc704075
(cherry picked from commit f278ca60e06da86c67f6a3865c290f8451657ce9)