We're still only generating the released versions and "current" when
we build with build-ndk-prebuilts.sh. Pass
Platform_version_all_codenames from make to generate the in-progress
platform versions as well.
Also move this over to soong.variables, since that's the appropriate
place for them. The Platform_sdk_version we were passing wasn't
actually being used before.
Test: OUT_DIR=ndk-out DIST_DIR=ndk-dist \
build/soong/scripts/build-ndk-prebuilts.sh
Bug: None
Change-Id: Iccb709f5c12309754073ac8f0d4bc365019dfcd3
59034511c5