Allow vendor-init-settable and public-readable to ro.config.low_ram

ro.config.low_ram should be set on Android Go devices by SoC vendors,
and the value can be read by vendor components.

Bug: 76132948
Bug: 75987246
Test: succeeded building and tested with taimen
Change-Id: I6ac98fa58cf641da4565d6277898fc5e5e6ceca1