openrisc: Use Kbuild infrastructure for kvm_para.h

All the headers but kvm_para.h use the Kbuild infrastructure to
get to the asm-generic headers.

Cc: linux-kbuild@vger.kernel.org
Cc: linux@lists.openrisc.net
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Jonas Bonn <jonas@southpole.se>