LU-506 FC15: move some headers to include/generated

In FC15 (2.6.40-4) the generated kernel headers have moved
from "include/linux" to "include/generated". Update configure
scripts and makefiles to include this new directory. In a
number of cases, Lustre code was including generated headers
directly, but this was not really needed.

Signed-off-by: Yang Sheng <ys@whamcloud.com>
Change-Id: Id2094d8318681aa5ea08b416dc764bcf03bd8595
Reviewed-on: http://review.whamcloud.com/1329
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Lai Siyao <laisiyao@whamcloud.com>
Reviewed-by: Niu Yawei <niu@whamcloud.com>