Cap the LRU position of broadcast receivers in bg restricted apps

Previously receiving a broadcast will bump the receiver's position
in the LRU list; now for apps in restricted bucket or background
restricted level, receiving a broadcast won't bump its LRU position.

Bug: 200326767
Test: atest CtsAppTestCases:ActivityManagerTest
Change-Id: I45ed2fed0a807a48e0096997d0e34f4867f1a6a7