core: Don't fail when system partition and reserved size are defined

[Preet23]

When BOARD_SYSTEMIMAGE_PARTITION_SIZE and
BOARD_SYSTEMIMAGE_PARTITION_RESERVED_SIZE are both defined, the build
will fail since it's defined in treble's common makefiles.

To avoid this, if the device has a custom system partition size
specified, set the reserved size to nothing and use the system partition
size instead. Be sure to warn the build user of this change

Taken from:- CypherOS/build@7bdc901

[yyl3866]

https://github.com/AOSP-KONA-MSMNILE-LAHAINA-KALAMA/device_xiaomi_cmi/tree/thirteen

[100% 1/1] analyzing Android.bp files and generating ninja file at out/soong/build.ninja
FAILED: out/soong/build.ninja
cd "$(dirname "out/host/linux-x86/bin/soong_build")" && BUILDER="$PWD/$(basename "out/host/linux-x86/bin/soong_build")" && cd / && env -i "$BUILDER" --top "$TOP" --so ong_out "out/soong" --out "out" -o out/soong/build.ninja --globListDir build --globFile out/soong/globs-build.ninja -t -l out/.module_paths/Android.bp.list --available _env out/soong/soong.environment.available --used_env out/soong/soong.environment.used.build Android.bp
error: vendor/aicp/build/soong/Android.bp:24:8: module "generated_kernel_includes": cmd: unknown variable '$(PATH_OVERRIDE_SOONG)'