base_system.mk: Package wifi.rc separately into the build

These contain a bunch of action triggers for setting some kernel flags
for wifi driver logging. Apex'es don't support .rc with action triggers,
so package it separately into the build.

Bug: 149909892
Test: Device boots up and connects to wifi networks.
Test: Manually verified that the .rc file is run on bootup.
Change-Id: I05f055ec68d47a1d158135f5454389a786884f9b