[POWERPC][LIBXC] Add missing HVM stubs.

Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>

--HG--
extra : transplant_source : %5B%A9%A9%F7%D5%F4%FF%16%85%00%06%B2%A0%B2%ECC%7Cy%D9

tools/libxc/xg_private.c

@@ -196,3 +196,15 @@ __attribute__((weak)) int xc_hvm_build(
 {
     return -ENOSYS;
 }
+
+__attribute__((weak)) int xc_get_hvm_param(
+    int handle, domid_t dom, int param, unsigned long *value)
+{
+    return -ENOSYS;
+}
+
+__attribute__((weak)) int xc_set_hvm_param(
+    int handle, domid_t dom, int param, unsigned long value)
+{
+    return -ENOSYS;
+}