s390/kvm: Split kvm_host header file

In order to generate asm offsets into kvm_s390_sie_block linux/kvm_host.h
is included in asm-offsets.c. This causes quite often header dependency
problems, since linux/kvm_host.h pulls in a lot of other header files.

Solve this problem and split out the hardware structure declarations into a
separate header file. Include only the new header file into asm-offsets.c
instead of linux/kvm_host.h. This is sufficient to generate the two asm
offsets required for kvm (__SIE_PROG0C and __SIE_PROG20).

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