s390/bios: Make the s390-ccw.img relocatable

The current bios sits at location 0x7e00000 in the guest RAM
and thus prevents loading of bigger ramdisks. By making the
image relocatable we can move it to the end of the RAM so that
it is getting out of the way.

Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Message-Id: <1425895973-15239-3-git-send-email-thuth@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
[Fixup build failure on 32 bit hosts]
