powerpc/kvm/book3s_pr: Fix compilation on 32-bit machines

Commit a413f474 ("powerpc: Disable relocation on exceptions whenever
PR KVM is active") added calls to pSeries_disable_reloc_on_exc() and
pSeries_enable_reloc_on_exc() to book3s_pr.c, and added declarations
of those functions to <asm/hvcall.h>, but didn't add an include of
<asm/hvcall.h> to book3s_pr.c.  64-bit kernels seem to get hvcall.h
included via some other path, but 32-bit kernels fail to compile with:

arch/powerpc/kvm/book3s_pr.c: In function ‘kvmppc_core_init_vm’:
arch/powerpc/kvm/book3s_pr.c:1300:4: error: implicit declaration of function ‘pSeries_disable_reloc_on_exc’ [-Werror=implicit-function-declaration]
arch/powerpc/kvm/book3s_pr.c: In function ‘kvmppc_core_destroy_vm’:
arch/powerpc/kvm/book3s_pr.c:1316:4: error: implicit declaration of function ‘pSeries_enable_reloc_on_exc’ [-Werror=implicit-function-declaration]
cc1: all warnings being treated as errors
make[2]: *** [arch/powerpc/kvm/book3s_pr.o] Error 1
make[1]: *** [arch/powerpc/kvm] Error 2
make: *** [sub-make] Error 2

This fixes it by adding an include of hvcall.h.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kvm/book3s_pr.c

@@ -35,6 +35,7 @@
 #include <asm/mmu_context.h>
 #include <asm/switch_to.h>
 #include <asm/firmware.h>
+#include <asm/hvcall.h>
 #include <linux/gfp.h>
 #include <linux/sched.h>
 #include <linux/vmalloc.h>