lint: generate options from kconfigcheck.toml

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.