lint: generate options from kconfigcheck.toml (MR 2412)

Now that we have moved the kconfigcheck configuration into pmaports
branches via kconfigcheck.toml, it is time to get rid of the hardcoded
list of valid "pmb:kconfigcheck-…" options for APKBUILDs. Generate it
from the kconfigcheck.toml of the current branch, too.

These options are passed from "pmbootstrap lint" to "apkbuild-lint",
which we run in pmaports CI.