scripts: compliance: Fix misdetection of Kconfig choices as undefined

This commit updates the KconfigCheck to add the Kconfig symbols from
both "config" and "choice" symbol lists to the defined symbol list, as
opposed to the "config" list only, in order to prevent any references
to the choice symbols outside the Kconfig files (e.g. in documentation)
from being reported as undefined.

Signed-off-by: Stephanos Ioannidis <stephanos.ioannidis@nordicsemi.no>