powerpc/include: Add opal-prd to installed uapi headers

We'll want to build the opal-prd daemon with the prd headers, so include
this in the uapi headers list.
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/uapi/asm/Kbuild

@@ -18,6 +18,7 @@ header-y += kvm_para.h
 header-y += mman.h
 header-y += msgbuf.h
 header-y += nvram.h
+header-y += opal-prd.h
 header-y += param.h
 header-y += perf_event.h
 header-y += poll.h