Mark libbnnmlowp as vendor_available

This is required by libRSCpuRef, which is a vndk-sp library. Since this
is a static library, vendor_available: true is enough.

Bug: 64425518
Test: BOARD_VNDK_VERSION=current m -j libRsCpuRef.vendor
Change-Id: Ica7d9dbf99111ff7ace24a773cf200e82a380639
1 file changed