iwlwifi: fix LED support Kconfig dependencies

If DVM or MVM are built-in but LEDS_CLASS isn't then the current
Kconfig will enable LED support and fail the build. Fix this by
making the LED support depend on LEDS_CLASS being built-in or,
if it is modular, only enabling it if iwlwifi also is.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>