Build sepolicy_tests for all build types

Currently the build target sepolicy_tests is only being built for Treble
devices. However, the tests performed are not specific to Treble
devices.

Unconditionally build sepolicy_tests regardless of Trebleized status.

Bug: 64612408
Test: Policy compiles
Change-Id: I1bf37f6e17a0bcfde451fe668e32798120a66043