util/lint: Add linter to keep selects out of Kconfig.name

util/lint: Add linter to keep selects out of Kconfig.name

While having select statements in Kconfig.name files is valid in the
syntax of the Kconfig language, having the selections split between the
normal Kconfig file and Kconfig.name files makes it harder to see what's
going on.

Kconfig.name files will now be limited to their original purpose of
selecting a particular board or board variant, not actually configuring
that board.

Signed-off-by: Martin Roth <gaumless@gmail.com>
Change-Id: I2aab78e296f2958e77a938b1afa40a25a6aa82b0
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78972
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Maximilian Brune <maximilian.brune@9elements.com>
Reviewed-by: Julius Werner <jwerner@chromium.org>