Allow redeclaring typeattributes

Allows partners to add a new attribute definition to their public
policy without causing a compatibility failure with the AOSP system
image.

Bug: 67092827
Bug: 37915794
Test: build and boot aosp_sailfish with new type declared in public
    policy

Change-Id: I015c26fa7c399423e8a6e7079b5689007d031479