KVM: s390: Fix storage attributes migration with memory slots

This is a fix for several issues that were found in the original code
for storage attributes migration.

Now no bitmap is allocated to keep track of dirty storage attributes;
the extra bits of the per-memslot bitmap that are always present anyway
are now used for this purpose.

The code has also been refactored a little to improve readability.

Fixes: 190df4a2 ("KVM: s390: CMMA tracking, ESSA emulation, migration mode")
Fixes: 4036e387

 ("KVM: s390: ioctls to get and set guest storage attributes")
Acked-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Message-Id: <1525106005-13931-3-git-send-email-imbrenda@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>