The patch change Legacy GSI (aosp_$arch_(a|b)) to inherit from
gsi_common.mk instead of treble_common.mk
It does not inherit from gsi_common.mk directy. The patch adds
legacy_gsi_common.mk to extend gsi_common.mk, and all Legacy
GSI inherit from legcay_gsi_common.mk.
The patch also removed treble_common*.mk.
Bug: 119747870
Test: flash aosp_arm64_ab-userdebug on blueline P
Test: flash aosp_arm64_ab-userdebug on walleye O-MR1
Change-Id: If54760484cc0937719c1336f1a4caac8468d2009
