pc-bios/s390-ccw: Move libc functions to separate header

pc-bios/s390-ccw: Move libc functions to separate header

The upcoming netboot code will use the libc from SLOF. To be able
to still use s390-ccw.h there, the libc related functions in this
header have to be moved to a different location.
And while we're at it, remove the duplicate memcpy() function from
sclp.c.

Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1499863793-18627-2-git-send-email-thuth@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>