s390,uapi: do not use uapi/asm-generic/kvm_para.h

It turns out that S390 shouldn't use uapi/asm-generic/kvm_para.h since it
defines the functions in its non-UAPI kvm_para.h file.

#including <asm-generic/kvm_para.h> will first pick up
include/asm-generic/kvm_para.h, which defines conflicting functions.

Instead, partially revert commit 0420c87e,
ungenericising this file and just inserting a comment to prevent the patch
program from deleting it.

cc: Yuanhan Liu <yuanhan.liu@intel.com>
cc: fengguang.wu@intel.com
Reported-by: Yuanhan Liu <yuanhan.liu@intel.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>