s390x/ipl: support extended kernel command line size

s390x/ipl: support extended kernel command line size

In the past s390 used a fixed command line length of 896 bytes. This has changed
with the Linux commit 5ecb2da660ab ("s390: support command lines longer than 896
bytes"). There is now a parm area indicating the maximum command line size. This
parm area has always been initialized to zero, so with older kernels this field
would read zero and we must then assume that only 896 bytes are available.

Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Viktor Mihajlovski <mihajlov@de.ibm.com>
Message-Id: <20211122112909.18138-1-mhartmay@linux.ibm.com>
[thuth: Cosmetic fixes, and use PRIu64 instead of %lu]
Signed-off-by: Thomas Huth <thuth@redhat.com>