Build ramdisk's build.prop with soong

Following the same pattern as existing soong build.props.

Bug: 378146476
Test: Diff'd out/target/product/vsoc_x86_64/ramdisk/system/etc/ramdisk/build.prop before and after this cl
Change-Id: I41503a0f8d8d0041b9975ae42b376026b4437db4