xen: remove unnecessary code from dataplane/xen-block.c

xen: remove unnecessary code from dataplane/xen-block.c

Not all of the code duplicated from xen_disk.c is required as the basis for
the new dataplane implementation so this patch removes extraneous code,
along with the legacy #includes and calls to the legacy xen_pv_printf()
function. Error messages are changed to be reported using error_report().

NOTE: The code is still not yet built. Further transformations will be
      required to make it correctly interface to the new XenBus/XenDevice
      framework. They will be delivered in a subsequent patch.

Signed-off-by: Paul Durrant <[email protected]>
Acked-by: Anthony Perard <[email protected]>
Signed-off-by: Anthony PERARD <[email protected]>