Fix some system property missing problem on aosp_* targets

Some PRODUCT_PROPERTY_OVERRIDES has no effect, ex.
ro.dalvik.vm.native.bridge=0 in runtime_libart.mk,
because gsi_common.mk uses ':=', not '+='.

Bug: 125829345
Test: build aosp_arm64-userdebug
Test: check the properties in /vendor/build.prop
Change-Id: Ib5e026069e7919fed8a00f905f3dbaa15042107f