qcow2: Extract code from get_cluster_offset() (Laurent Vivier)

qcow2: Extract code from get_cluster_offset() (Laurent Vivier)

Extract code from get_cluster_offset() into new functions:

- seek_l2_table()

Search an l2 offset in the l2_cache table.

- l2_load()

Read the l2 entry from disk

- l2_allocate()

Allocate a new l2 entry.

Some comment fixups from Kevin Wolf

Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
Signed-off-by: Kevin Wolf <kwolf@suse.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5003 c046a42c-6fe2-441c-8c8c-71466251a162