UAPI: Put a comment into uapi/asm-generic/kvm_para.h and use it from arches

Make uapi/asm-generic/kvm_para.h non-empty by addition of a comment to stop
the patch program from deleting it when it creates it.

Then delete empty arch-specific uapi/asm/kvm_para.h files and tell the Kbuild
files to use the generic instead.

Should this perhaps instead be a #warning or #error that the facility is
unsupported on this arch?

Signed-off-by: David Howells <[e-mail]>
cc: Arnd Bergmann <[e-mail]>
cc: Avi Kivity <[e-mail]>
cc: Marcelo Tosatti <[e-mail]>
cc: [e-mail]

arch/ia64/include/uapi/asm/Kbuild

···
 # UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
+generic-y += kvm_para.h
+
 header-y += auxvec.h
 header-y += bitsperlong.h
 header-y += break.h

arch/s390/include/uapi/asm/Kbuild

···
 # UAPI Header export list
 include include/uapi/asm-generic/Kbuild.asm
 
+generic-y += kvm_para.h
+
 header-y += auxvec.h
 header-y += bitsperlong.h
 header-y += byteorder.h

include/uapi/asm-generic/kvm_para.h

···
+/*
+ * There isn't anything here, but the file must not be empty or patch
+ * will delete it.
+ */