ro.build.expect.* sysprops are created in a separate rule

This change is required to unify the build rules for */build.prop files;
The rules shouldn't have partition-specific actions.

Bug: 117892318
Test: m
Manually inspect ro.build.expect.[bootloader|baseband] props in
vendor/build.prop

Change-Id: I3b29b2728f779a9d7e1d71a5aa69b02ea940b3c6