libcutils: route to ashmemd

If libcutils is not a VNDK version and /dev/ashmem is not available,
then ask ashmemd for opened fd to /dev/ashmem.

We rely on SELinux policy to determine what's allowed to open
/dev/ashmem directly.

Bug: 113362644
Test: device boots (in selinux permissive mode)
Change-Id: I93c4fa6044b0bfa5282097c6c32139a8d8f67deb