Add soong module for aosp_{arch}

aosp_{arch} build GSIs for release, whereas gsi_{arch} build GSIs for
compilance test. System images of aosp_{arch} are supersets of system
images of gsi_{arch}, with a few exceptions (userdebug sepolicy).

This adds a Soong module for aosp_{arch} targets, named
aosp_system_image, enabled only when building GSI.

Ignore-AOSP-First: depends on frameworks/base change submitted only on
internal

Bug: 381019944
Test: build, TH
Change-Id: I81b50a038c29bbd1a61fed8044cb600bd22b45e4