Add a ramdisk stub for targets that referred to goldfish's arm32.mk

there is a check that requires the ramdisk to be nonempty.

Bug: 250696437
Test: presubmit
Change-Id: If3918ec1eb0e6263ed845e48c7415755c0cfc832
Signed-off-by: Roman Kiryanov <rkir@google.com>