Mark fs-verity support for ext4 userdata if first_api_level >= R

fs-verity is required for new devices launched with R. This change
remove a manual setup for vendors going forward. The original fs mgr
flag still allows old devices to opt in, which can only to be done
manually because of kernel dependency.

Test: build
Bug: 150034150
Change-Id: I152b63d7889153d41f29677f72074afb1881b65d