Mark libprocinfo vendor_avaialable.

libprocinfo belongs to vndk-cap. Mark it vendor_available to enable vndk
abi stability checks on it.

Details: https://android-review.googlesource.com/368372

Test: mm -j64

Bug: 38244611

Change-Id: Ib79c7e3bdde1c7d3cd9f2bb95c284b4690a22ebb