Retroactively add identity V2 to 5.xml.

Identity V2 is introduced in R, but Android R VINTF does not support AIDL
versions. Hence, we only specify identity V2 in compatibility_matrix.5.xml
in Android S+ branches. In Andorid R branches, the matrix implicitly
specifies V1. SingleManifestTest.ManifestAidlHalsServed has an exemption
for this.

Bug: 178458001
Test: pass
Change-Id: Iaf6947a31cc34d81d3a1d6655b85af00baab90f3