A condition can be but on a prompt to make a symbol conditionally
user-assignable (visible).
Kconfig note:
'default's don't care whether the symbol is visible (has a prompt with a
satisfied condition) or not. 'if'/'depends on' just puts the same
condition on all the properties, disabling both the defaults and the
prompt at the same time. That might make it look like they're connected.
Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>