[S390] vmcp cleanup

A number of small changes to vmcp:
 - Change preferred email address.
 - Use PRINT_xxx machros from debug.h like most s390 drivers, define
   "vmcp:" as PRINTK_HEADER and wrap error message at column 80.
 - Add error number to error message.
 - Update copyright, as I touched this file.
 - Small whitespace diff.
 - Use mutex instead of semaphore (Thanks Heiko for the patch)
 - Don't register debug feature on failure.
 - Check debug feature registration on init to avoid a potential oops
   on unload if the debug feature could not be registered--> 2 more
   messages.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>