[S390] Get rid of cpuid.h header file.

Merge cpuid.h header file into cpu.h.
While at it convert from typedef to struct declaration and also
convert cio code to use proper lowcore structure instead of casts.

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