[cfi] Adjust RLIMIT_AS by CFI shadow size.

CFI (control flow integrity) implementation is using a MAP_NORESERVE
allocation of up to 2GB is size. Only a tiny portion of it is backed
by physical memory. Take this into account when setting RLIMIT_AS for
media services.

Test: no immediate effect; CFI shadow increase for 48-bit aarch64 can
      be reapplied w/o breaking android boot.
Bug: 64293803

See https://android-review.googlesource.com/#/c/platform/bionic/+/424903/.

Change-Id: I8d4e780a8579f3102f97abe0f5c9bf8f3dee3d2f