kconfig: fix __enabled_ macros definition for invisible and un-selected symbols

__enabled_<sym-name> are only generated on visible or selected entries, do not
reflect the purpose of its introduction.

Fix this by always generating these entries for named symbol.

Reported-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Arnaud Lacombe <lacombar@gmail.com>