s390/early: Copy last breaking event address to pt_regs

In case of an early crash the early program check handler also prints the
last breaking event address which is contained within the pt_regs
structure. However it is not initialized, and therefore a more or less
random value is printed in case of a crash.

Copy the last breaking event address from lowcore to pt_regs in case of an
early program check to address this. This also makes it easier to analyze
early crashes.

Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>