Enable the mainline supplicant build
flag in the trunk_staging config.

Bug: 365585450
Test: Manual test
       1. m
       2. adb root; adb remount; adb sync
       3. adb shell ls \
          apex/com.android.wifi/bin/
          # should contain the binary
Change-Id: I3e813480103f4318c8d0b3d7b13b86db877c9eef