add llndk|vndksp.libraries.txt to vndk_package

List of llndk and vndk-sp libraries are written in the txt file so that
they can be available at run-time. The information is used by
libnativeloader to configure the classloader-namespace specially for
vendor apks.

Bug: 64882323
Test: build 2017 pixel devices. check that the two files exist on
/system/etc.

Change-Id: Ifbe339a5862f6ef57a8213a14a022765ccf77283