Push wpa_supplicant modules down to the leaf product config.

Since 558477c0b2a5a7db679c1ad7551d43e6364d1df2 in
external/wpa_supplicant_8 we don't need those modules if
WPA_SUPPLICANT_VERSION is not set by the BoardConfig.mk.

Change-Id: Idca392a07689ed398b9f876d31212d042801a8ed