Preserve hal_cas_server attribute

It's used in CTS neverallow tests.

Addresses:
Warning!  Type or attribute hal_cas_server used in neverallow
undefined in policy being checked.

Bug: 66910049
Test: build
Change-Id: Ia185f266fc1e3cb87c39939fdd45d02efa6c2c94
Merged-In: I1092aff40da9dcf09bd044400bedd1f549eb7e38