e2fsprogs: disable e4defrag in host variant

e4defrag from e2fsprogs 1.42.13 encounters these build errors on RHEL5.8 hosts:
e4defrag.c:197:2: error: #error sync_file_range not available!
e4defrag.c:201:2: error: #error fallocate64 not available!

It's possible to fix these problems, but we don't use it on the host
anyway, so just disable it.

Signed-off-by: Hollis Blanchard <hollis_blanchard@mentor.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>