LU-5971 llite: remove struct ll_ra_read

LU-5971 llite: remove struct ll_ra_read

Remove the unused function ll_ra_read_get(). This makes the struct
ll_ra_read members lrr_reader and lrr_linkage and the struct
ll_readahead_state member ras_read_beads unnecessary so remove them.
In struct vvp_io replace the struct ll_ra_read cui_bead member with
cui_ra_start and cui_ra_count.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Id54ad063d917fb9e13a6708a87c940450c4af506
Reviewed-on: http://review.whamcloud.com/13347
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>