Bump up the max persisted uri grants

With scoped storage, more apps will need to rely on
SAF to get access to non-media files. Allow more grants
by bumping up the limit to 512.

BUG: 149370983
Test: m


Change-Id: I65c71c404bd09fec5849d3e9e7a8cfafe6631a63
(cherry picked from commit 5a293b8e)