[S390] Fix IPL from NSS.

IPL from NSS didn't work because the memory detection routine omits any
memory sections with a size lower than what MAX_ORDER defines.
This causes the detection routine to skip the first memory segment which
has a size of 1MB. Which later on will let the kernel think that there
is no memory available at all.
Since in addition the z/VM memory increment size is 1MB force MAX_ORDER
to be 9, so we can support 1MB segments.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>