Add BUILD_BROKEN_TREBLE_SYSPROP_NEVERALLOW

A new sysprop neverallow rules are mandatory only for devices launching
with R or later. For devices already launched, neverallow rules can be
relaxed with adding following line to BoardConfig.mk:

BUILD_BROKEN_TREBLE_SYSPROP_NEVERALLOW := true

Bug: 131162102
Test: Set PRODUCT_SHIPPING_API_LEVEL := 30 and try building with
changing some system_public_prop to system_internal_prop
Test: m cts sepolicy_tests

Change-Id: I44a83af19b18b4116f83a3d5dc929f28bb8870ce
Merged-In: I44a83af19b18b4116f83a3d5dc929f28bb8870ce
(cherry picked from commit 06fb4554)