Generate kvm hypercall functions with a macro instead of duplicating
the more or less identical code seven times. This also reduces number
of lines of code.
However the main purpose is to get rid of as many as possible open
coded error prone register asm constructs in s390 architecture code.

For the only user of kvm_hypercall identical code is created
before/after this patch (drivers/s390/virtio/virtio_ccw.c).
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
Link: https://lore.kernel.org/r/20210713145713.2815167-1-hca@linux.ibm.comSigned-off-by: Heiko Carstens <hca@linux.ibm.com>