s390/vmcp: split vmcp header file and move to uapi

Split the vmcp header file and move the device driver internal
structure to the C file, and move the ioctl definitions to the uapi
directory.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>