staging: lustre: discard cfs_cap_t, use kernel_cap_t

lustre only sends 32bits of capabilities in on-the-wire RPC calls.
It current strips off higher bits and uses a 32bit cfs_cap_t
throughout.
Though there is a small memory cost, it is cleaner to use
kernel_cap_t throughout and only truncate when marshalling
data for RPC calls.

So this patch replaces cfs_cap_t with kernel_cap_t throughout,
and where a cfs_cap_t was previous stored in a __u32, we now
store cap.cap[0] instead.

With this, we can remove include/linux/libcfs/curproc.h

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>