block: Introduce bdrv_dirty_bitmap_granularity()

block: Introduce bdrv_dirty_bitmap_granularity()

This returns the granularity (in bytes) of dirty bitmap,
which matches the QMP interface and the existing query
interface.

Signed-off-by: John Snow <[email protected]>
Reviewed-by: Max Reitz <[email protected]>
Reviewed-by: Eric Blake <[email protected]>
Reviewed-by: Stefan Hajnoczi <[email protected]>
Message-id: 1429314609[email protected]
Signed-off-by: Stefan Hajnoczi <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>