Add soong system image configs

USE_SOONG_DEFINED_SYSTEM_IMAGE is true when the target is using a
system image defined in soong.
PRODUCT_SOONG_DEFINED_SYSTEM_IMAGE is the module name of the soong
defined system image.

Bug: 350599535
Test: lunch aosp_cf_x86_64_phone_soong_system-trunk_staging-userdebug
      && m
Change-Id: Ic5c848fb649a5a61de1a5a253438b2d77d200a6b