s390/early: Dump register contents and call trace for early crashes

s390/early: Dump register contents and call trace for early crashes

If the early program check handler cannot resolve a program check dump
register contents and a call trace to the console before loading a disabled
wait psw. This makes debugging much easier.

Emit an extra message with early_printk() for cases where regular printk()
via the early console is not yet working so that at least some information
is available.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>