arm64: vdso: Supply vDSO bounds to seccomp syscall filters

Pass the vDSO text bounds to seccomp, so that they can be passed to
seccomp filters via struct seccomp_data.

This allows seccomp filters to treat syscalls from the vDSO
differently from other syscalls.

For now This discrimination should not be relied on for any
security property, since nothing stops userspace moving the vDSO
under a filter's feet.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>