Refactor sysprops to use gd/os/system_properties

Have one method to access system properties regardless of OS so
we can remove OS dependencies in code where sysprops are
currently being used. system/gd/os/system_properties was created
with that in mind, so utilize the gd abstraction in
osi_property_get/set and refactor sysprops to use osi_property.

Bug: 239956470
Tag: #refactor
Test: m
Change-Id: I639960af94965a7f151b2c5ec6583f419b59a8a8