staging/lustre/fld: prepare FLD module for client server split

Split FLD server from client, fld_{handler,index}.c are not compliled
unless server support is enabled.  Do not include dt_object.h or
lustre_mdt.h in lustre_fld.h and fix the minor breakages caused by
this elsewhere.  Generally cleanup includes in lustre/fld.

Signed-off-by: Liu Xuezhao <xuezhao.liu@emc.com>
Signed-off-by: John L. Hammond <john.hammond@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-1330
Lustre-change: http://review.whamcloud.com/2675


Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>