Convert -j to a reasonable parallelism for kati

When running makeparallel in non-ninja mode, which is used when running
kati with USE_GOMA=true, convert -j to a reasonable parallelism value
the same way ninja does.

Bug: 34392351
Test: make -C build/make/tools/makeparallel makeparallel_test
Change-Id: I9aee4dd2a3b0f2b1c2c10087be83f7b2b06f4368