hw: Convert from BlockDriverState to BlockBackend, mostly

Device models should access their block backends only through the
block-backend.h API.  Convert them, and drop direct includes of
inappropriate headers.

Just four uses of BlockDriverState are left:

* The Xen paravirtual block device backend (xen_disk.c) opens images
  itself when set up via xenbus, bypassing blockdev.c.  I figure it
  should go through qmp_blockdev_add() instead.

* Device model "usb-storage" prompts for keys.  No other device model
  does, and this one probably shouldn't do it, either.

* ide_issue_trim_cb() uses bdrv_aio_discard() instead of
  blk_aio_discard() because it fishes its backend out of a BlockAIOCB,
  which has only the BlockDriverState.

* PC87312State has an unused BlockDriverState[] member.

The next two commits take care of the latter two.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/hw/arm/z2.c b/hw/arm/z2.c
index 9b38a2b..1735547 100644
--- a/hw/arm/z2.c
+++ b/hw/arm/z2.c
@@ -21,7 +21,6 @@
 #include "sysemu/sysemu.h"
 #include "hw/block/flash.h"
 #include "sysemu/block-backend.h"
-#include "sysemu/blockdev.h"
 #include "ui/console.h"
 #include "audio/audio.h"
 #include "exec/address-spaces.h"
@@ -337,7 +336,7 @@
 
     if (!pflash_cfi01_register(Z2_FLASH_BASE,
                                NULL, "z2.flash0", Z2_FLASH_SIZE,
-                               dinfo ? blk_bs(blk_by_legacy_dinfo(dinfo)) : NULL,
+                               dinfo ? blk_by_legacy_dinfo(dinfo) : NULL,
                                sector_len, Z2_FLASH_SIZE / sector_len,
                                4, 0, 0, 0, 0, be)) {
         fprintf(stderr, "qemu: Error registering flash memory.\n");