The filesystems already implement REQ_PEEK, but do not fully
use the new filesystem cache code yet. (Because it isn't committed
yet..) REQ_PEEK should be disabled for them until they do.
This indicates to VFS that they are not annotating their cache
blocks (in VM) with inode number/offset info, and therefore mmap()
shouldn't succeed on any of their files. (Most importantly exec()
won't fallback elegantly otherwise.)
Change-Id: Ic57ee422864b4bbc031eadba32973270907b02fd
75c5fe4c26