pnfs: Automatically select blocks & objects layouts

Just like files-layout, blocks & objects layouts are part of the
NFS 4.1 protocol and should be automatically selected if NFS_4_1
is selected. The small problem is that these depend on other
Kernel support being present, while files only depends on NFS
itself.

This patch removes from the user choice the presence of objects
and blocks layout. But makes sure these are selected only if
the depended subsystems are present in the Kernel.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Acked-by: Peng Tao <peng_tao@emc.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>