LU-744 clio: save memory allocations for cl_page

LU-744 clio: save memory allocations for cl_page

It used to allocate 6 piece of memory to create a page:
 - top cl_page, llite & lov page slice;
 - subpage, lovsub_page & osc_page.

This patch will allocate top cl_page, llite and lov page slice in
the same piece of memory, similar to sub pages, so that only 2
memory allocations will be needed for each page.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I1c4dd0541bda23e7d739131f73bcd895b8dd2c13
Reviewed-on: http://review.whamcloud.com/4943
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>