Do not hide VNDK prebuilts from make

Flattened APEXes don't install modules hidden from make. This CL unhides
VNDK prebuilt modules to make VNDK APEX work correctly. The suffix for
VNDK prebuilt is still omitted if the version of prebuilt is same with
BOARD_VNDK_VERSION.

Bug: 149542527
Test: build arm64 GSI and flash
Test: Set BOARD_VNDK_VERSION and build
Change-Id: I54a7c14c93eccfefc81603ec3bb474a031bc55af