xen-blkback: expand map/unmap functions
xen-blkback: expand map/unmap functions

Preparatory change for implementing indirect descriptors. Change
xen_blkbk_{map/unmap} in order to be able to map/unmap a random amount
of grants (previously it was limited to
BLKIF_MAX_SEGMENTS_PER_REQUEST). Also, remove the usage of pending_req
in the map/unmap functions, so we can map/unmap grants without needing
to pass a pending_req.

Signed-off-by: Roger Pau Monné <1c35b25b17252e1e5021df00666589fc74f64580@citrix.com>
Cc: Konrad Rzeszutek Wilk <da3a51b335cef0eb0e2c329c5ef6bcd6acef687a@oracle.com>
Cc: 196a79ea1bad81d8c954adf793448b0a45442f28@lists.xen.org
Signed-off-by: Konrad Rzeszutek Wilk <da3a51b335cef0eb0e2c329c5ef6bcd6acef687a@oracle.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs